This game has got to be nearing completion. At least 60-80% complete since the major holdup for years has been the inability to properly code and sprite the bosses/new complex enemies - they've added tons of new enemies recently too and seem to be mostly refining the level design to accommodate new enemies now.
In the Christmas stream in the OP they show off a partially completed Sparkling Scorpio boss fight and the Strike boss with Ultimate Armor equipped (which I'm assuming is the Sigma Fort boss fight for Strike) - upon defeating that version of Strike you gain the Ultimate Armor.
They have shown 6 of the 8 maverick fights so far on stream or on youtube. The 4 on youtube you can specifically search for are Crystal Rafflar, Warfare Milodon, Hurricane Hoatzin, and Neurohack Mosquito. On stream they showed off months ago an incomplete but fully functional Plasma Puffer boss fight (they were missing a desperation attack at the time and wanted to make sure the boss could be beaten without taking a hit and with base X and Zero) and I know the area for Plasma Puffer (the sewers) was completed years ago but they are likely remaking it now to be up to par with the rest of the game. Sparkling Scorpio's area looks done and it's just the boss fight which needs to be fully finished with a desperation attack in addition to more regular attacks and better movement.
I have a feeling they won't show off Force Starfish's area or boss fight beyond the one video we saw of them beginning development for it on Facebook. It's the area we've seen the least of so far. Even Warp Vulpex's area we've seen more of. I doubt we'll see Warp Vulpex's boss fight either but they did show that they are upgrading all the sprites for that area to keep it in line with all the new sprite work they've done and better level design.
The only major issues I see standing between this and release now seems to be how big Sigma's area is gonna be and how far along they are in developing it. They showed off a new area in a stream a month or so ago that had a Wily logo in the background so I'm assuming they've at least started Sigma's fort.
Also in the stream they added the X1 armor (with X3 type airdashing) complete with the Hadouken which can be used regardless of your health (but is dependent on x buster weapon energy now) - the Hadouken can also be used in the air. Same button presses as a regular Hadouken in Street Fighter. If you have full HP and full x buster weapon bar you can perform a Kamehameha which does more damage and lasts for multiple seconds.