Is there a TI expansion that will play like Eclipse, or plans to make such an expansion?
Not that they've announced, no. I haven't had a chance to play Eclipse myself (though I would be interested to try it.) However, from what I've gleaned of the rules, it seems like making an expansion that converts TI3 into Eclipse would involve a lot more rules changes than an expansion generally implies. What you're really asking for here is a new edition of TI that plays like Eclipse.
Or do I have to buy and find space on my poor crumbling book shelf for Eclipse itself?
If that's your only recourse, then yes, you need to find room for Eclipse on your shelf.
I will happily wait a few months for a TI, small box game, that uses existing TI tiles and plays like eclipse. Doesn’t even have to be original, a complete rip off would actually be perfect.
I don't honestly believe any such product is coming out at all. Certainly not within a few months. You could always buy Eclipse and then make a print and play total conversion to retheme the components in TI fluff style. I may even be interested to see such a homebrew project, if I ever get around to playing/owning Eclipse myself.