TYPO3 Core

In principle, this is a good idea - but it is a bad idea to bind this at SYS_LASTCHANGED since this value does not necessarily contain the needed information

for example, if the page contains a plugin which generates a "random" output, you can't send 304 by comparing with SYS_LASTCHANGED - and TYPO3 simply does not know if an INT-cObject has not changed since the last request.

The only soltion for that would be a really careful cache configuration (by the Developer using the right cObject and the Editor, by defining those values in the cache control settings) - but this is also not trivial, since taking a page from the TYPO3 cache does not necessarily mean, it has not been modified.

WIll it continue or will it stay closed ?

BTW, Sigfried is wrong : TYPO3 knows if there is INT objects, and no cache headers at all are sent in this case.

There is also the ETag handling which is already generated and send by TYPO3, but not respected when receiving an ETag.
https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching

This also affects current master.