PHP 7.0 is EOL and no longer patched or supported by its developers so unfortunately that's not really a viable platform. I keep hearing that option bandied about so just wanted to address that issue.
PHP 7.1 will reach EOL in December. Many shops will have already begun the pivot to 7.2 from an infrastructure and support perspective.
Re: OSTicket v1.11; Running a custom-tweaked, beta version of software is a-ok for smaller shops and individuals - but no organization is going to deploy unstable software - because the entity producing it (in this case OSTicket) will understandably not offer proper, full support. Because it's not the stable product platform. Which, for the record, is a completely reasonable position for a software provider to take.
OSTicket (by which we should really say Enhancesoft) have painted themselves into a proper corner on this one. I came to this thread hoping that there would be some clarification from developers on a roadmap (even if informal) but there seems to be no news unfortunately. There are just rocks on one side, and hard-places on the other of "not supported" which really recommend investigation of alternative ticketing solutions.