Whether or not QLink will ever operate jets is a commercial decision that I am sure the honchos at QF will make without our advice or opinions.
Whether pilots could transition direct from the Q400 to LHS jet is a no-brainer. ANYONE who is a competent pilot on a turbo-prop can do it, and not take very long to do it, either. Even from older generation analogue turbo-prop to glass jet is do-able for anyone of normal intelligence and ability.
As for CASA: Where, in their old or proposed new rules, does it say an ATPL must have prior jet-experience to fly a jet? Plenty of pilots have gone from turbo-prop to jet commands, having done just the minimum required line training - and lived to tell the tale.
IF it were to happen, it would be the insurers who would insist on a core of type-experienced check and training people to kick it off. Unless the incumbent Chief Pilot had appropriate jet time, CASA would probably insist on a type-experienced 'Fleet Captain' in the interim and would of course have to approve the checkies. So CASA could make it hard for a few, but not really for QF in the grand scheme of things. Other than that, CASA would be on thin ice if they tried to dictate that all Captains had to have prior jet time over and above the ICUS requirements in the regulations.
IF the pilots union had any teeth it would allow a very limited number of direct-entry checkies in, perhaps on fixed-term contracts, then see them off with a nice thank-you party after a couple of years.
Sadly - if history is anything to go by - should it happen, pilots will fall over themselves to accept whatever terms are on offer.