Here's the historical closing and opening dates for McKenzie Pass. I believe ODOT made a decision last year to never open the gates before the 3rd Monday in June so bicyclists could at least count on the gates staying closed until then. I'ts not supposed to be much of a snow year this year. If you could wait until February or early March to set a date, you should have a better idea of when it will be open.

I concur that riding Hwy 58 from east to west would much more pleasant. I'd also suggest you ride the around Mt Batchelor. That climb up to Bachelor is a doozy, but the scenery is magnificent. (The route you have marked between the Inn at Seventh Mountain and Sunriver is gravel BTW).

I wouldn't recommend FS 21 to Summit Lake on road bikes. Cross bikes with wide tires maybe.(Read paragraph no. 3 on the link)