Orlandu, Eileen and Majin fina are the Big draws. Any of the 3 could be a very Big jump in the quality of any party
Two of the three won't be out by December, if they decide to go with 3 Rainbow Crystal deal for 10k Lapis(Like they did in JPN) with Majin Fina being a maybe. Basically you're potential pool of 5* Base characters would be all we have now, plus Snow, the FFBE Exclusive, Giglamesh, and which ones come from the two FFZero events. They may also do a Christmas special set. So add it on top of the current lot of non 5* Base units too.
Basically, if it does parallel JPN, they'll be stopping right before the next big set up upgrades, ala Orlandu, Eileen, and Majin Fina if offering the 5* Crystal Deal this Holiday season. They'll be taking a lot of Lapis right before the next big Power creep wave comes out, where I feel like it would be better to save for a chance at those, rather than the greater shot at the current selection of 5*
Even after Olrandu drops, Luneth is almost on par with him on Global due to no double materia stacking.
I wouldn't say Luneth is close to on par even without stacking. It may knock Orlandu down a peg, but Luneth isn't going to be able to exploit elemental weakness like Orlandu can nuke a boss into oblivion.
But going in Luneth and Lightning's favor is they don't need Materia to be great. Both of them are better out of the box than the rest. They don't need Dual Weilding TM or to farm their own/others for the elemental chain. One of the things to consider when looking at Orlandu, Tidus, and Eileen since Altema takes TM's into account with ranking