The update should not cause too much drama for HTC, as GPE devices run a stock build of Android, plus a few minor tweaks to incorporate any additional hardware built in by the OEM. In the case of the One M8, HTC has to get those dual rear-facing cameras working properly.
Versi tweets that while they are targeting for a release of an OTA this month, he will release additional information when launch is closer.
Are you rocking a One M8 GPE device? How has it treated you recently?