This is a very difficult question. We know somewhat his preferences, because he worked on implementing ALGOL 60 [0][1], but unfortunately we are blocked by a bit of incommensurability; in that time, garbage collection was not something that could be taken for granted. As a result, what he might have built in our era is hard to imagine.

That said, he did have relatively nice things to say about Haskell [2] and preferred Haskell to Java:

> Finally, in the specific comparison of Haskell versus Java, Haskell, though not perfect, is of a quality that is several orders of magnitude higher than Java, which is a mess (and needed an extensive advertizing campaign and aggressive salesmanship for its commercial acceptance).

I imagine that he would have liked something structured, equational, declarative, and modular; he would have wanted to treat programs as mathematical objects, as he says in [2]. Beyond that, though, we'll never know. He left some predictions like [3] but they are vague.

[0] https://en.wikipedia.org/wiki/ALGOL_60

[1] https://www.cs.utexas.edu/users/EWD/MCReps/MR35.PDF

[2] https://www.cs.utexas.edu/users/EWD/transcriptions/OtherDocs...

[3] https://www.cs.utexas.edu/users/EWD/transcriptions/EWD12xx/E...