Fwiw, between the ages of around 53 to a little over 57, I schlepped the Yamaha CP300 around, which is almost identical in weight to the MP11. I replaced it with the 52 lb. Yamaha CP5 for a few years after that. I finally threw up the white flag of surrender around age 60 when I purchased the original Nord Piano 88.
Actually it was less about the weight then the bulk. It was getting too unrealistic trying to squeeze into small bars and restaurants with tiny set up areas with this huge beast. In addition to a pair of speakers.
I had a Yamaha branded soft bag/case that fit the CP300 and CP5. It's no longer made because I'm guessing they got tired of messing with returns from people hauling around 72 lb. keyboards with it. The bag had wheels but I mainly would use my Magliner Gemini Jr. dolly. I could always manage it by myself except for a few instances I recall where there were a lot of steps.
I still have the CP5 but it resides strictly in the home office now with the CP4 seeing all gigging duties. Before I got the CP4 I was looking at a more substantial soft bag and found the German made Soundwear -- actually recommended by someone on this forum who was using it for his CP5.
You might contact them directly as I'm guessing they'd have a model that would fit the MP11.
The CP4 has certainly caught my eye, but it is wicked expensive here in Argentina (I can get a Nord Piano 3 and a QSC K8.2 speaker for the same amount of money). Otherwise it would be a no brainer.
Wow, this is really something ! If that's the case, I would go with the Nord. It's the same weight (which you probably already know) as the CP4.