I can add some info here.
Mach4Lite is to be sold bundled with a hardware motion device, Smoothstepper, PoKeys, etc Basic 4 axis control for simple routers, mills. No scripting, no Modbus, none of the advanced stuff, just basic CNC for simple devices. Price set by the hardware company that sells it.
Mach4Hobby is to be everything you know in Mach3, sold to hobby users for $200. Some kind of price deal will be made for recent purchasers, details not yet decided. Brian is really sincere in support of the hobby guys and giving them the best deal he can, and still stay in business. This is running now, but needs motion control device support. Ethernet SS works now, USB to come. All of the current motion device companies are working on plug-ins, Dspmc, kflop, gailil, and several I dont recall.
Dont worry about paying for new versions, vs bug fixes. By Brians view Mach2 to Mach3 was an upgrade, all the other releases were bug fixes. It will be a long time before there is a Mach4 upgrade that costs money. Same with the wizards. There will be more wizards, like Plasma, WoodRouter, Turn, etc. Each will cost $75, but you will never need to buy more than 2, then all are free after that. I am not sure which wizard will be next, probably Turn, since I don't have a plasma, and don't do wood, and I will be writing it.
Mach4 commercial is wide open, lots of talk between Brian and Todd, nothing in stone yet.
The use of Lua for I/O is more to replace brains than PLCs. PLCs are modbus devices.
Yes, commercial users will go up a couple hundred dollars, still way under the 10K-20K price for things like fanuc or centroid.
The screen design is new, and will take a bit to learn, but it is so damn cool it will be worth it. Screens now can have all the modern GUI widgets, like tabbed dialogs, list boxes, combo boxes, tree controls, etc. Its dead easy to use, and Lua is not hard. I have played with it, but not written a real screen yet, but like everything else 'real soon now'
The open GL requirement is for a version that has been out for several years, it should not be an issue with any video card.
The linux issue is complicated Brian does not want to get into the linux support business. His best hope is for an OEM to take that on, but he will likely do a rigid, single distribution strategy.