Probably the largest barrier to using D is needing to hook up with existing C++ code. D is already doing tolerably well with that. For example, the front end of the D compiler is written in D and hooks up to the 3 backends which are in C++.

We're working at making it much better. Recently added, for example, is the ability to catch exceptions thrown by C++ code.

Thanks! And how is deployment to the platforms that run on common mobile handsets?

I don't know the state of that at the moment. You'll have to ask on the D forums.

Last time I looked at support for ARM it was quite lacking (no exception support, the compiler needing patches to compile, test suite not passing). There were people working on this, but unfortunately it didn't seem a top priority for the community.

I'm not sure why this is, as D would seem a perfect fit for writing stuff for the Raspberry Pi and similar; the other usual suspects have focused on ARM support almost from day 1.

Lending a hand there it's been near the top of the list of "things I'd like to do if I had some spare time" for a long time, but I haven't come around that yet. It looks like a fun project, and not one you come across often. Want to write "Helped port a major programming language to ARM" on your resumé? Hurry up!