If you're talking about projects where people are following the letter and spirit of the license, and publishing their code, but it's a pain to use... that's not really something you can control with a copyright license. The correct answer in that case is to not use that code and treat projects that rely on it as technical debt.
If you mean that the SaaS provider has a private fork of someone else's code, and won't publish that fork... well, AGPL already exists for that. But here's the thing: in order for any license to close this loophole, you need to create a licensing term that obligates the user to publish private forks. These terms will inevitably either restrict the user's freedom to run the program, or the user's freedom to modify the program. I don't see why we should be calling restrictions on either freedom[0] to be Free Software or Open Source.
My personal feeling is that companies that are adopting "SaaS-loophole" copylefts are looking for the street cred of being source-available, while still being able to wield copyright in the way one would with proprietary software. Hence the Commons Clause that bans commercial endeavors on top of the already difficult-to-comply-with Affero clause. If you want to be paid, just... demand payment.[1] That's what proprietary licensing is for, and you are never going to close the "SaaS loophole" in FOSS while still remaining in the spirit and letter of FOSS.
The thing about SaaS is that it wasn't invented this decade. Even back in the 80s and 90s when FOSS was novel, you had massive IBM mainframes that could be partitioned, virtualized, and rented out exactly in the same way Amazon does today.
[0] GPL and weaker copylefts are tolerable because said licensing provisions only trip on distribution. Ordinary users do not need to worry about GPL compliance until they want to give someone else their code. This is a feature, not a bug.
[1] Are FOSS support contracts still a thing?