Some of us that want the OTA, want it so we can ROOT!
For the Eris at least, HTC/VZW have not yet pushed an OTA that replaced the bootloader. That doesn't mean it is impossible, but only that they have not been in the habit of doing that. So, the possibility exists that they could do an "OTA" that fixes up all the leak phones to the OTA-2.1 code ... but leaves the 1.49.xxx bootloader intact. No root for leakers (using existing methods) if that happens.
Having said that, I don't know why they would even be doing that: releasing an OTA that does nothing substantial other than replace the bootloader, as it has been widely reported that leak-V3 and OTA-2.1 are essentially identical in all regards except the bootloader. That's just shy of Big Red issuing a press release saying "here you go, please root your phones!"
The MR1 and MR2 (or "RUU") PC-based software, did replace the bootloader, although the upgrade from MR1 to MR2 overwrote the original bootloader with an identical copy (1.47.xxxx).
It's a curious thing: does HTC/VZW want rooters, even though they publicly disavow such activity?
After all, they could have installed the 1.49.xxxx bootloader as part of the OTA-21 - that would have prevented anyone not rooted who accept the OTA from using the prevailing method to obtain root afterward. And the time frames involved certainly allowed HTC/VZW to do just that - it's not like they were unaware that the root leak occurred. ( My own pet theory is that HTC management knows exactly who the root leaker is - and that he did it with their approval; but that's a different post.)
Perhaps HTC/VZW have been thinking that because the OTA goes to 99.99% of the Eris customers, and a failure during IPL/SPL (bootloader) replacement results in a hard-bricking of the phone, it is simply too dangerous a method to be used with 99.99% of their customer base. ( If the bootloader is intact but the rest is trashed, I suppose the phone could be reflashed by the VZW Refurb techs using methods similar to "Goldcard", but if the bootloader is whacked, you can't even do that. ).
The other 0.01% of Eris owners will either be a rooter, or willing to give a RUU/MRx install a try, and are more likely to accept the consequences of a failure during flashing, as they make an "active" choice to attempt the method(s), rather than having it forced onto them (as the OTA does).
All conjecture at this point. If I were to bet, I'd bet that no "custom OTA" will be released for leaker-Vx handsets - ever.
eu1
ps I've got root