If the creators were prepared or able to make update guarantees, they would have already; it would have only made sense. They can't. If you're interested in becoming a Tool in the hopes of a greater update schedule, I can only view this as foolhardy; one can only assume that the creators are already doing what they can.
I've seen webcomic artists make update schedule guarantees in return for donations. In general, it doesn't work; they find out that they can't keep up with the schedule, or the donation rate doesn't keep up for very long. I think it would be foolhardy to attempt this sort of thing with such a history.
So . . . I guess these are my suggestions.
1 - Reguide your thinking. Your subscription isn't actually for Erfworld comics; it's for bonus material (+merch credits +secret forum access). Make your decision whether this is worth a subscription. (In particular, the regularity of bonus features would probably play a role--I would think it wise for the creators to post Toolbox update information where non-Tools can see it, in the interest of making this information available to those considering.) Remember, you get the same comics whether or not you subscribe.
2 - Wait a bit. You'll have more data going forward to see if Erfworld updates more regularly in a post-Tool universe, and make a decision accordingly.
3 - If you'd like to support the comic without making a regular commitment, there are a lot of options available. One-time donations are possible, and there's already merchandise available. Buy Book 1 when it comes out. You'll still be supporting the comic--possibly more than the Tools are, given that they're using their Toolbox credit to buy merch and have it spread across several PayPal fees to boot--but without any regular commitment, and certainly not more than you feel like giving at any point.
I can understand your concerns; however, I feel it's more logical to adjust your thinking than to have the comic adjust to your expectations. You're much less likely to end up disappointed.
(I apologize if my tone is a bit . . . cold? I just got back from Star Trek; I think Spock is affecting my writing patterns. Always did love that guy . . .)