OK, I hadn’t expected that, and there was no mention in the section added to NEWS.md for the #18457 branch. Thanks for the info!
That still doesn’t mean that a short form, keeping the constraint closer to the use of the typevar might not be useful to make things easier to read for mere mortals 
I think a useful short form might simply mean that S{T;T<:U} would be equivalent to S{T} where T<:U.
Array{Array{T} where T} would be equivalent to Array{Array{T;T}}, and Array{Array{T}} where T would be equivalent to Array{Array{T} ; T}.
Are there any parsing or semantic issues with that approach?
Anyway, no matter what the syntax, I’m very much looking forward to this in v0.6! Thanks very much for this big advance!