'...should have been in OTU...'
Possibly, though 'should have' is perhaps a bit strong. Putting the emphasis on gene-tech (necessary for clones/replicants/GELFs) and cyberware wouldn't produce the same universe at all, in the same way as having instantaneous J-drive, or FTL comms would make the OTU unrecognisable.
Nevertheless, the hooks and features of all those systems would still allow good games to be run, they just wouldn't be
Traveller, in my book, they'd be TransHuman Space, or CyberPunk, or some other milieu/genre.
In the OTU-as-is, I think the major reasons for the lack of development of clone/skinjob/cyber tech are social (like the situation with Psionics). Perhaps the ethical questions about 'replicant rights' have been answered with 'They have the same rights as other sentients', so skin-jobs just aren't worth making when there's already an abundant and free source of sentients to oppress. Maybe they went through a period of cyber-enhancement and ran up against something like CP2020's 'cyberpsychosis' which was deemed too dangerous to risk.
It may be that you could make a good story out of the burgeoning of these industries as mores change over time, or of the clash of cultures when the Empire scouts out a Pocket Polity which has gone down the route of genetic or cybernetic enhancement of the organism. Herbert in his
Dune series had lots of secret societies that broke the rules about thinking machines and messing with genomes; their conflict with the mainstream was a rich source of story. Some similar themes are explored in Holistic Design's
Fading Suns RPG.
Gyrojet weapons were pretty much dropped from development because they couldn't compete with conventional firearms. Maybe they'd be back on the cards if we were fighting in 0-G environments, but I suspect they'll be competing with lasers by then, so they're still marginal. OTU does, though, as Andrew says, have gyrojet weapons. One of the problems with having an explosive payload do most of the damage (rather than the K.E. of the round) is fitting the payload in. Sure, we've 20mm grenades being developed for deployment now, but magazine capacity is always going to be restricted, and no one is expecting direct hits on evading targets with 'em.
Stargates. I'd argue against "any civ that could create a J-drive...could make a J-Gate" pretty strongly. The energy, engineering and resource requirements for such an undertaking would mean that a Gate of J
n would be several tech levels higher than a Drive of the same number. That's
if the very nature of J-space doesn't mean that the concept of a 'tunnel' through it is largely meaningless. Add to that the consequences of the gate being shut down for whatever reason (no ship plying this incredible trade route for profit would have a J-drive) and you have a strong argument for there being no or very few Gates.
Now, possibly, these things (along with competent, sensible-sized computing

would have been in
Traveller from the beginning if the RPG phenomenon had waited a decade or so, but they weren't, and, for me, they should be the strange and either distasteful or awe-inspiring, not the familiar and accepted. It's a flavour thing. A game with Reps and Wi-Ref and Stargates doesn't taste
bad (I've enjoyed games with all of these things in them), it just wouldn't taste like
Traveller to me.