Honestly, what needs to happen is this.
1. PDF costs X
2. Hardcover costs X + Markup.
Buy the PDF, if you want the hardcover pay for it. As errata get rolled out, the PDF automatically gets upgraded to the new errata.. and you can re-download it. If you want an updated hardcover, pay for it again. Being honest, I feel this is more or less how it is now, but there's no way to print on demand an updated book with all errata included for most publishers.
The real change needs to be access to the play testers and employees of the firm. If you want to drive a sub model, then make all the freebie rules clarification and sage advice stuff plus more UA and other content behind a paywall. The folks that paid for it would subsidize the time between editions.
I'm sure WoTC tried some of this with an insider sub, but the problem in my mind with Insider was that it was chained to 4E, which didn't have the best reputation to begin with and made Insider's flaws more glaring.
If you did the Insider model well with the right game behind it.. it would be fine and perhaps all the silly interpretations that come out of things like sage advice would be higher quality.
I know I wouldn't want to spend time answering player questions if it wasn't driving profit on some level and I'd treat it as a distraction rather than a boon.