it has also "Values in the map document's coordinate system"
That's the older ArcMap product, not ArcGIS Pro, Esri's new flagship GIS package that is replacing the older ArcMap product. The quotation I cited came from the ArcGIS Pro documentation. The option that was in ArcMap appears to have been dropped from the new ArcGIS Pro.
Anyway, if a ridiculously costly software as Arcgis lacks such an option, what can I say...
Well, you might say that indicates Esri users have other priorities. If a very expensive package like ArcGIS Pro dropped that option, most likely the reason is that Esri customers did not want it.
One of Esri's design goals for Pro was to focus on commands that people use and, as part of simplifying the UI and making the package easier to learn, reducing the number of commands and options that were not used.
That's a typical goal for any company introducing new generations of very large products. A new generation is a good time to clean out unused commands, making judgement calls in cases of commands that only a very few people use.
Anyway, should we be sending suggestions ever for things we have asked before, as a reminder? If yes, how much time after the first suggestion should we do this?
The best advice for how to get your way is in the Suggestions page. Nowhere does that page advise repeatedly submitting the same suggestion. Given the very detailed information in the Suggestions page, it seems to me that if repeating the same suggestion from time to time had any value, it would be one of the tips provided. Therefore, I'd recommend a focus on what the Suggestions page advises.
One of the things the Suggestions page advises is to avoid having tunnel vision. There are often many ways of accomplishing a goal in 9, and fixating on just one method can prevent you from seeing alternative ways of doing what you want. As the Suggestions page puts it, "don't jump to the assumption that something cannot be done and so a new feature is required."
For example, if you want to Goto a location in projected coordinates, you don't need to select a point to go there. You can have quicker workflow.
What I would do is to work with a map (almost always more efficient for the use of multiple layers it provides), and have a drawing layer in that map that's in the projected coordinate system I want, with one point in the drawing. I'd have that drawing opened in its own, undocked, small-sized window as well, so when I picked the point in it with an Alt-click it will stay picked, with the Info pane automatically popped up anytime I clicked on that drawing's undocked window.
You can then do whatever you want in the map window and all the layers it has, and whenever you want to go to some projected coordinate, you just click on the small undocked drawing window, enter the coordinates you want into the Coordinates tab, and then you can Ctrl-click the Drawing's tab in the map and it will zoom to the new location of the point.
For repetitive operations, how does that compare in click count to using a GoTo box?
For any GoTo XY operations, you still have to enter the X, Y coordinates you want, so that's the same amount of keyboarding whether you enter them into a GoTo box or into the Info pane coordinates. The number of mouse clicks ends up being the same, or very close to the same, as using a GoTo box.
There's a click to choose the undocked drawing window for context and a click for the Coordinates tab in the Info pane, as compared to one or two clicks to choose a GoTo command from a menu. There's a Ctrl-Enter to accept the new coordinates as compared to a click or two to do the same in a GoTo command, and then there's a Ctrl-click to zoom the map to the new location. For repetitive work it's one more click and might even end up being the same number of clicks. You can leave the drawing in the map so that once you create it, it's always available, even in future sessions with no need to redo. One advantage of using the Info pane approach is that the initial coordinates of the point are visible there, to show beginners what coordinates look like in that projected coordinate system, so that might reduce user errors in some cases.
Given a simple way to GoTo a projected XY coordinate, combined with the rarity of use (when's the last time any Geocaching or other location web page published coordinates other than Latitude Longitude?), based on the tips in the Suggestions page it seems to me that the best odds for advancing such a niche desire would be to discuss how it comes up and why it should be prioritized over something else and is genuinely necessary compared to existing workflow possibilities. Priorities, as the Suggestions page comments, are important.
For example, I personally like the idea of Goto functionality, but I'd prioritize first, a text goto where the text was automatically searched for by a web geocoder like Google or Bing. You could then just enter "Buenos Aires" to go there. That also automatically gets you street address GoTo and Lat / Lon using a variety of formats, and it provides some automatic protection against entry of nonsense or wildly wrong coordinates.
I'd give second priority to an offline GoTo using Lat / Lon decimal degrees, and third priority to offline GoTo using Lat / Lon in various other formats, like degrees, minutes, seconds. But I wouldn't prioritize arbitrary projected coordinate system entry. Instead, as a fourth priority I'd suggest the same options Esri provides, just so that Esri people who also use 9 would have the comfort of the same options.
We don't know why Esri didn't implement arbitrary projected coordinates in a GoTo XY that already allowed some projected coordinates. My guess is that they had zero user interest in that, or that they had so little user interest that it was not worth it for them to harden the dialog against misuse by people who don't understand projected coordinates. That's also something to consider, as there's always a cost to provide protections against people misusing advanced options.
Anyway, this essay is offered in the spirit of encouraging suggestions by discussing a example, and to encourage taking advantage of the Suggestions page tips to get what you want.