Think of it this way, if GAE has a feature that MG does not, then MG might wish to implement it. However, if they do not know about this feature in MG, they may end up implementing it differently! Having the same thing done a different way in both engines is a huge pet peeve of mine, since there's no reason that has to happen, such as with Lua timers, GAE had them long before MG and they were well known to exist, yet MG created their own syntax. Had they used the same syntax, MG scenarios with timers would be compatible to GAE and vice versa.
Likewise, with tooltips, they can either create their own method, or they can use GAE's existing method. This has NO DISADVANTAGES and numerous advantages, such as allowing mods to work on both engines, allowing documentation to be easier (just document one feature for both engines instead of one each, despite doing the same thing), modders can adapt to the other engine easier (same syntax instead of having the learn new syntax), and in the event that a merge should ever resurface, it will be easier, as there's no need to support legacy code then.
It's called constructive criticism, and it overall brings the better for the game (sadly, a merge would bring a lot more of that "better").