I was thinking about this today when looking at the xenscripts bridge.
My planning goes out at least 3-5 years and preferably 10...my site has been up for 17 years.
I just cannot build something on an add-on which may be here today and gone next year!
There may be some solution to this. On one hand, you could have it as core.....or you could have an officially backed add-on, where if the author stopped writing and supporting it, XF would agree to update it or take it over.
Other than that, the only solution I can think of is an open source model (with donations) where the source code is shared and a number of folks have enough interest in it going on...that one feels fairly confident the basics will work.
In my case, the basic setup (login to XF, then you are logged into WP) would probably do the job. XF would be the forum, WP would be articles, QA, reviews and other stuff.