MTS already has a lot going for content content creation(ex. vehicles, food items, standalone parts, guns, etc) and one of the things that would help make content packs would be to allow for actual blocks, slabs, blocks with specific roles(ladder, stairs, furnace, etc).
Already decors take a lot of resources, they are technically place-able entities, we have to ask our users to use other mods for various blocks. I believe it would be a great addition! It would bring more creators to decide on using MTS, because it would have most features for starting to create content!
The disadvantage though, blocks would most likely require .json models exported from BlockBench, and have minecraft limitations of 3x3x3m, and rotations of 22.5 only. But that wouldn't be that much of a deal.

On my side, I have an Asphalt Paving Machine. I would love to be able to be independent on blocks; so i don't have to tell people to go download that mod for asphalt, roadworks etc.