IIUC, since #4468 (341735eb8f42e898cf9d4d130709471e5d01abe2) has been merged, i.e. v0.10, the Bitcoin Core has no means to send GetBlocks messages to its peers.
How long should we support the means to handle GetBlocks messages from other peers?
Barring any exploits or attacks, I think the answer should be "forever".
It's not because Bitcoin Core stopped using these messages that they're gone from the protocol. For many simpler applications it's probably the easiest way to synchronize blocks.