Just to confirm, is the Wheeltop Gex the same RD just with longer cage to clear the bigger cassette? From the looks of it, if the eGR cage is removable, then it can accommodate a long cage for better in-spec 50t shifting, correct? Similar how you can swap out the cage on a GRX 812 RD for a Garbaruk cage.
If so, either LTwoo or another vendor should design a different cage for the eGR. 
Wheeltop offers the GeX with two cage lengths one rated to 46t and one to 51t (the one I'm also using). I've heard second-hand that they've said it should work on 52t also but they had some problems on some bikes and decided not so officially support that.
More importantly, the GeX is a different RD than the road TX version. So likely the geometry in the main links is different to allow for a wider range cassette as well. The TX only supports 36t
Given that the LTWOO eGR DOES work up to 50t, just not optimally, I'm not sure a longer cage would help all that much. I haven't observed problems with chain wrap (taking up the slack) which is usually what is helped with a long cage. For example, tike the Garbaruk one I had on a Force RD before the LTWOO to reach 50t. It also DID work, but didn't shift quite as slickly as I would have liked (and why I'm playing with other options) I think it is a geometry challenge in the motion that leaves the upper jockey wheel either too close to the 50t or too far from the 11t
To be clear, the LTWOO does work all the way to 50t. It is just not optimal. You must step one cog at a time in the last couple. For rated capacity and a Di2 prepped frame, I'd happily use it again (and it's sitting on a shelf with that intent)