A concern about the luggage roller. Smaller cases will tend to slide around and fall between the two uprights. The structure of the case or package it's carrying is what keeps the bungees from pulling the handle down and trying to close. The wheels are quite hard and transfer vibrations to whatever it carries.
I've used the Magna Cart, which is sold in BJ's for around $40. My work computer doesn't want me to browse BJ's, so here's an eBay link instead: http://www.ebay.com …nal-Luggage-/181383460348
I know your initial ask was for portability. The problem with carrying gear around in public like this is it's a target for snatch-and-grab thieves. Pardon my being blunt, but chasing a $30 solution to carry a $10k lens strikes me as penny-wise, pound-foolish. I would save up to get a proper camera backpack, roller case or hybrid roller backpack to keep that glass in your hands instead of some thief's. A backpack would be my first choice because nobody is likely to snatch it off your back, but given your pregnancy, something like the Ape Case ACPRO4000 should fit the 500 plus other gear, and give you a choice of rolling it behind you or wearing on your back as desired. And when the baby comes you'll have room in the laptop compartment to carry some clean diapers and bottles for your new child.
Otherwise, I would recommend the stroller solution to keep the lens in front of you and in your sight, rather than a trolley that gets dragged behind you. And find some way to secure the case to the stroller.
