Deduction regression or improvement?

[Meta via Digitalmars-d]

On Tuesday, 8 March 2016 at 22:35:57 UTC, H. S. Teoh wrote:
> IMO, this *should* compile and infer T == const(SomeStruct) as 
> the common type of a and b.  But I'm not sure whether or not 
> this is a regression.

Does template type inference do implicit conversion? I thought it 
did not, and thus would expect this example to not compile.