Replying...

1) It depends. We operate some very large J1.5 sites for many years now without an issue because we can control everything from the server setup all the way up to the actual content (with K2).

2) Sure, but the choice for no b/c upgrade path was bad. Thus why K2 still supports J1.5 all the way up to 3.x.

3) Not really. K2 has supported 3 versions already. Adding a fourth won't be an issue when the time comes.

4) That's a known limitation. Those who know what they're doing can still operate a secure server with PHP 5.6.

In fact with the latest K2 it has been easily shown that any extension can be backwards compatible (some still are) and look great at the same time. Plus, people who want to move their content to a newer Joomla release will have an easier upgrade path if they switch to K2 because unlike com_content, K2 shares the same DB structure across all Joomla versions. Which was not magic either way, just common sense.

Thank you.