We prohibit resold licenses mainly to stop scamming on eBay and other auction sites - people were getting ripped off. We will not provide verification that a license is valid to someone that is not the license holder, so there's no way for the buyer to actually know if the license is valid or not.
Old-school Threads license holders are still under the use terms of that license - it's per-domain instead of per-install.
Regarding what will happen to Threads... 6.5.1 is indeed the last planned update, but that doesn't mean there won't be a 6.5.2.
We will continue to support both Threads and Classic for quite a while after the new product has been released. When the time comes to drop support, it will be noted well ahead of time.
We may choose to make future bugfix releases depending on the nature of the bugs. For example, UBB.classic 6.7.2 has a nasty problem with the CSV parser in the importer, so we're releasing 6.7.3 some time in the next week or two that corrects the problem.
(Related note: Support for the 5-series of both Classic and Threads is being dropped on March 15th. After that date, the only aid that we will be prodiving in regards to those old versions will be helping to upgrade it. <img src="https://www.ubbcentral.com/boards/images/graemlins/wink.gif" alt="" /> It's likely that the same policy will be adopted when we choose to end support for Classic and Threads.)
Regarding the code hacking bit in the license... hm, that phrasing is a bit odd. My understanding of our intent is to allow descriptions on how to modify the code, but prohibit distribution of premodified files. Third-party add-ons that do not contain any of our code are fine - there are plenty, some even for sale. I'll bring this up and see if we can get that clarified.
