It would need to:
1) Be compatible with VB6 (take any existing source code and be able to compile and run it)
2) Update the language to at least VBA7.1 standard (and therefore support 64 bit)
3) Ideally have the Microsoft ActiveX controls built-in rather than as ActiveXs (move away from ActiveXs)
4) Still support ActiveXs (for 3rd party/old controls)
5) Ideally not need a separate VB Runtime
6) Update the look and feel of both apps and the IDE (same as you can do in VB6 by adding a Manifest)
7) Option to compile to 64 bit (see 2 above), ideally supporting 32bit ActiveXs. If ActiveX support isn't possible then 64 bit compile with built-in controls only (see 3 above).
8) Include Multi-threading (as you can do in VB6 with a multithread DLL).
9) Be DPI-aware (as you can do in VB6 with replacement controls)
10) Possibly minor language enhancements, such as Try/Catch error handling.
"VB6 is not just a language. VB6 is a language, a runtime, a platform library, a tool/IDE, and an ecosystem tightly packaged together in a way that made all of them work well together. " - Paul Yuknewicz, Microsoft