I would bet Sinclair will try to get Grit shifted to KPDX 49.3 so they can add Comet to 47.3. But you’re right, Portland is running short on subchannel slots. KOIN still can add, but the # of diginetworks not carried here is growing.
Comet TV is going to be on two Sinclair stations in ID, Boise & Lewiston. I would guess Portland will have it, but if it ends up on KUNP, no one outside the Portland metro area will receive the channel OTA.
2.1 is 720p so KATU could add a 2.4 for Comet, but Sinclair might have a two subchannel limit per station. If so, their options are limited. Would be ironic if they have two stations in Portland but can’t get their own network on here.
I don’t know much about technical specs. But most stations running 1080i on their x.1 channels usually carry two subs max. A lot running 720p on x.1 carry more than two. KPXG Ion 22.1 looks fine in 720p and they run six subchannels. Many cord-cutters want quantity (diginetworks). For quality, keep cable or satellite.