If you remove probability from plausibility and simply reduce it to possibility, then just about anything becomes plausible. It would be plausible that if I buy a Powerball ticket today I will win.
That's too much a stretch for me and seems to render plausibility useless as a word. Possible or impossible would be all that would be necessary to use.
If you go the other way you can see it in action as well. In criminal court you need to find someone guilty beyond a reasonable doubt. A lot of people misunderstand that and treat any possible doubt as reasonable. If someone is 99.9% likely to have done it, but there's that 1 in 1000 chance that it was someone else, is that doubt reasonable? I would say no, but if you divorce probability from things like you are doing with plausible, then that 1 in 1000 chance becomes reasonable/plausible.
Anyway, I doubt we will change each others opinions here. I'm glad to have had this discussion and I wish others here on the site were as pleasant to speak with. It makes conversations much more enjoyable.