I'll second the request for the Enterprise-E. Given that Worf had no trouble showing up for the TNG movies, it would have been nice to see the Enterprise-E make a visit to DS9. Particularly after the Enterprise-D had been there twice.
Many forget that the TNG Episode Birthright is a crossover, with the Enterprise-D stopping at DS9 and Bashir hanging out with Data. So it wasn't unprecedented for the Enterprise to crossover. I'm sure Frakes and a couple other TNG cast members could have been talked into making a cameo, and with a line of dialog about Picard being on Earth for some meeting, you don't even need Stewart.
It was definitely a missed opportunity, particularly given the other crossovers that have happened throughout Trek.