I doubt
anybody outside UA's product team and perhaps its chosen seat maker / design partner (and maybe some Airbus folk) would know this right now. I certainly don't.
There are in essence three ways this could go (assuming we rule out the old and now very uncompetitive 2-2 layout):
1. The uniquely 'Vantage' approach as per some pics above, with alternating rows of 2-2 and 1-1
2. The direct aisle access model as seen in UA's widebody Polaris and also as typified by JetBlue's A321LR Mint and the Vantage Solo, although most if not
all seat makers now have (or are working on) a similar 1-1 layout
3. The X-factor of a very different and unexpected seating layout – for an example of this, here is the Access concept by Factorydesign, which combines a high-density 2-2 layout with flatbeds and 'no step-over' access to the aisle.
I think everybody here would like a proper 1-1 layout, as if the current Polaris window seats were zapped with a shrink-ray for
just long enough until they fit into the A321's cabin footprint; doors may be optional, some people like them (and JetBlue has 'em) and some don't.