actually the "no mirror" part is what is so appealing to me. I think the X-mount is currently the closest flange distance in APS-C/35mm. For me this is much more important than compactness.
@nerwin I agree with others. Just shoot with what you have and save up to buy a used mirrorless at some point. Mirrorless depreciate pretty quickly so it's pretty easy to get into a system for a few hundred bucks. Whatever system is gathering dust, whatever system you stop getting excited for whenever new exclusive glass is announced - that's the system to abandon; the one you don't use.
But I don't think you need to worry about either technology going anywhere any time soon, and for the foreseeable future either will be a fine investment.