A year ago of this publication and MSFS2020 has improved its SDK and SIMCONNECT a lot. We have some news that can tell us about this?
I don't know where you read Simconnect has "improved a lot". The SDK as a whole surely has, but Simconnect hasn't changed much, and it's still missing exactly the same features we were missing back then which are:
1) the ability to temporarily interecept keys/buttons in the sim and prevent the sim to get them ( event masking, currently still not working ).
2) all the menu/text functions which are used to create the in-game menu, used by so many add-ons.
About #1, we recently got word from Asobo they don't want to add that feature as it was in FSX, because they fear of add-ons causing conflicts between them and/or the sim and, instead, are considering a completely new approach, since they DO realize the ability to do that is required for doing add-ons other than the simplest one which you can find right now.
Some popular add-ons ( not just GSX ) used a full event masking ( you press a key/button and the sim won't get it, even if it's normally assigned ) used it to allow, for example, full keyboard input in an FMC keyboard, so you could just type instead of clicking buttons. While this might not be *stricly* necessary for a traditional FMC, think about an real A350/A380, which use a FULL sized PC keyboard as input method: without event making, an user would be required to click on the 3d keyboard, when he could just use the real keyboard in front of him, which is really silly. That's why event masking is required to create serious add-ons.
About #2, nothing is telling they'll ever bring those features back so, we are currently using a custom menu to do our tests but, we are thinking a completely new and more immersive approach, which might not even require opening a menu to begin with.
But that's besides the point, in addition to the lack of features in Simconnect, we still need to do a complete update of all models in GSX, especially human characters, which can be made so much better in MSFS, and that takes time, more than it took on FSX/P3D, because the detail level is higher and the modeling must be on par.