CMH might come first because they only have DL/F9/WN and LCK-MCO on G4. Personally I don't want any more ULCC in IND!
WN is the only one running Orlando (either airport) daily from Columbus. DL is Saturday-only, 319/M88/E75 depending on season, F9 is (I think) 3x/week, and G4 is 3-5x/week.
I don't think they are done with those markets. They will of course continue to connect current points in the network but they will also open up new markets not served.
I can dissect the routes you've provided to MCO. CMH is highly unlikely due to the choice of opening CMH and the current opening of PIT, DAY even more unlikely than CMH due to obvious reasons, MDT in an awkward spot between PHL and BWI, ABE not as likely again due to current operations, ROC could happen but there's other markets to expand in first, ALB likely after more major markets are added due to the lack of LCC's and service overall, SDF unlikely and if BNA opens more unlikely, LIT could happen but not to MCO, OKC maybe due to lack of LCC service and service overall, and ICT not likely right now. What routes are likely for NK and MCO is hard to tell, like I said eventually I wouldn't rule out these thinner markets for the future, but there's still larger markets that need to be covered, I suspect BNA will open this year, NK could do an A319 MCO-BNA.
DAY has openly said they're in talks with NK and I feel like there'd be an opportunity there. I toured there a couple weeks ago and the airport employee escorting us said they're happy with the Southern expansion, but want to move West and claim they have the traffic to fill an LAX flight.
You'd have to believe CMH is talking to NK as well. CAK is actually closer to CMH and DAY than PIT/LBE is and there's a big gap in the Midwest where NK doesn't fly; F9 also opened CMH and PIT on the same day last year, so I don't see what the issue would be with the cities three hours apart.
I've always thought FLL would be a target for either NK or B6 from CMH, though.
A310/319/320/321/333, ARJ, BN2, B717/722/73S/733/734/735/73G/738/739/744/757/753/767/763/764/777, CR1/2/7/9, DH6, 328, EM2/ERJ/E70/E75/E90, F28/100, J31, L10/12/15, DC9/D93/D94/D95/M80/M88/M90/D10, SF3, SST