As the author of the Share to Speech app, I can tell you that it is unlikely that SoundGecko like app will appear. As you are probably aware, it was not withdrawn from the Windows Phone Store, but from all platforms.
If you quote their service provider NeoSpeech (or any other good service like Ivona), you will see that it is pretty expensive game to offer such service. They offered too much for free and it didn't make sense for them to continue (my guess, official reason is that they want to focus on Omny Radio, but why would they shut down their service if it was making money for them as long as it worked, and especially for the app that has less than 10 downloads per day on Android).
So, it is likely that every app that appears (well not just for WP but for every phone out there) will have to use phone's speech engine, which is probably better on WP than on other platforms. But there comes another catch. If you want the screen to be off during the speech, you have to implement the background player. So you are limited to something like 20 MB of memory, and the speech is memory intensive, so things become tricky. And then the background player is completely different app from UI app, and as in the speech changes happen quickly, it turns into the nightmare to sync them. All in all no one implemented that till now except me, and from financial side I think it has not paid off, but it was still an interesting effort.
Things that you can realistically expect - no new cloud speech apps, maybe some app with background player, and more likely just some new apps that use local engine with screen on (which is pretty easy to make and it is strange there aren't more of them).