Well I don't see why DX11 would help much. Adding DX11 support doesn't flip a switch and you get great performance. Actually it doesn't boost the performance by a lot as far as I know. From the switch itself I wouldn't expect more than a single-digit percent improvement. Maybe if someone skilled in writing shaders would jump into the fray there might be some further improvements but even then I don't think that this is the engine's bottleneck. Way more important than the simple featureset are how LOD, culling and in general the scene management is handled - that's where the real bottlenecks and performance improvements are. That's also why the DX11 switch in Unity did nothing groundbreaking in terms of performance...

So while DX11 support definitely should be on the list for future improvements I don't think this is what holds 3DGS down. I as described think the first engine related problem to address is the general workflow and toolset...