When you say multi-project do you mean enough staff to have 2 games in full production at the same time? Or simply that more than 1 project is currently in some stage of development at the studio? If 20 people are working on story, concept art, and early prototypes for Project A while 300 are deep in production on project B, is that "multi-project" per your definition?
At the absolute minimum I think it's guaranteed that they've got the capacity to do 1 full production and 1 pre-production project at the same time, I don't think this is in question. Maybe 1 full production of a larger title and 1 full production of a smaller title simultaneously? For example, the rumored GoW DLC/stand alone title and Corys game could both be in full production right now. I do think that with all the hiring that SIE studios have done over the last few years that they could be capable of 2 full simultaneous productions. Admittedly, of all the SIE multi-project studios I listed above, SMS are the one I'm least certain about.
Even if we only think they're doing 1 full production and 1 pre-production at a time, I think the list of games I projected out earlier can still be achieved. How? By doing all the pre-production while the other game is in full production. We had a tweet from a SIE dev not too long ago talking about pre-production and production timelines. I wish I could recall the specific figures, but IIRC it was something like 2-3 years for pre-production and 2 years of full production for a AAA title these days. So in my earlier list of projected SMS games this gen, here's how the timeline could work out:
2018: GoW ships. Also Ragnarok and Corys game go into pre-production
2021: Ragnarok was supposed to ship, but got delayed
2022: Ragnarok ships. Pre-production on the next mainline GoW begins
2024: Rumored GoW smaller title releases
2025: Cory's game ships. Next mainline GoW game goes into full production.
2027: New God of War mainline entry ships
1 year after the above mainline GoW game drops, they could drop a smaller title as well
So looking at the layout of the above timeline, Ragnarok was originally planned to ship after a 3 year total dev cycle (pre and full production) and wound up taking 4 years with a delay. In the above timeline, Corys game gets 4 years of pre-production and 3 years of full production (7 years total). Then the next mainline GoW game gets 3 years of pre-production and 2 years of full production (5 years total). The smaller entries/DLC don't interfere with the production cycles of the mainline games, in this prediction as the studio has the capacity to handle them both.
So going by the above breakdown, I think that's a perfectly reasonable time table of dev time for those projects given what we know of how Ragnarok was supposed to play out, and based on the info that the dev posted about pre/full production cycles.