That's a big part of the problem for WP8, (and 7 for that matter), there's such a huge market for Android (and now somewhat lesser iOS share) that there's very little incentive to port anything across to the minute market share they do have. And that's the same, I've got a S4 and TF300T tablet, no point holding my breath for a WP7 port of JMRI...
The other annoying thing about WP in general is you can't even use the (locally run) web based version of the throttle, either, as IE won't allow IP : port addresses.
I succumbed and made the jump to Android also, no point sticking with a market share that's in single digits still (WinPhone's first quarter of 2013 is 3.2 percent market share) virtually zero app support and unable to run most of the 'big' apps.
I think it would be a case of having to roll your own on this one.