nice idea- our machines are bigger, but could see advantages of similar setup...
thoughts- yours are obviously up to the task as its already proven- but- plating around the fork hole/leveling bolt bolt access holes might be good as thats about the highest stress point, and is cut out, think i'd opt to put the rollers just outside the pockets again for strength(and ease of 'steering') but i really like the wide footprint- should a roller go thru the floor, no chance of machine tipping...
we used to have a bunch of NATCO and Moline gang drills, converted with massive rockford drill heads... 15' tall, 6'x8' bases and we made big 'skates' to trailer them thru the shop on- each skate had 4 needle bearing supported 4" rollers with 2" pins, and the skates ended up 5" thick. these machines tooled weighed close to 50,000 and I saw cement pop a couple times under the rollers- my biggest worry was if one went THRU the floor, the machine would be damaged at a minimum, or literally fall over- so once machine was up on the skates i'd bolt wood full width across it using leveling holes- should a roller break thru, would have both a wood cushion and only 1/2" of drop till the wood would catch it, preventing it toppling... other guys that moved them usually wouldnt take the time to add wood, just pulled them on the rollers- luckily no one ever broke the floor and flopped a machine over... but several times one end of the skate would bust thru, hanging things up... your tube idea with the rollers integral is NICE- makes a lot of sense in many ways- built in 'shipping feet' to spread loads out on trailer, anti tip, easy side fork access, etc... really good setup.
forks pocketed too are smart- one of our guys was forking a new haas off a trailer, table wasnt clamped- was on a slight incline, table started rolling, weight shifted, machine slid when table hit the stops, off the forks she went- luckily missing everyone and the trailer, but they absolutely destroyed a new machine. had the table been bolted(ball bearing/no brakes on x/y, haas' NEED tables secured) and/or fork pockets existed, it couldnt have slid off the forks...
we dont have the big drills anymore, all the semi wheels have been drilled on single spindle cncs the last 15 years or so- much slower than our old 20 spindle geared heads (drilled all 10 lugholes and all 10 3" handholes at once- 3" coolant lines!), and our big iron/steel vertical broaching jobs all went overseas/machines to the scrapyards, so we havent moved much big stuff in a long long time... biggest we have now is the vertical lathes, but they are usually in the 25-35k range, and we boom them from the top... however if the big jobs ever come back, will definitely be wanting to fabricate some roller skids like these- even if just tubes that our skates could be pocketed into