Hi. (Or Guten Morgen. I've just okayed pages of legal stuff in German. I can speak "Holiday German" when I visit .... but not legal German)
I'm the bloke working on the open source replacement BASIC which is at https://github.com/paulscottrobson/6502-Basic . There is a reason for the name. It's a cross 65xx platform version. So it will run on a 65C02 (anyone who wants it), a 65816 (with Lenore Byron's project in mind) and the extended 4510 and take advantage of each. Currently I'm working towards loose Microsoft compatibility. Then adding nice stuff like named procedures. Then adding specifics for the Mega65.
That's version 2. I really don't like BEGIN/BEND and the DO LOOP. So we will have WHILE/WEND and REPEAT/UNTIL and IF/ELSE/ENDIF multiple lines and so on.
Most of the core is done. There are a few improvements to that. Firstly it does maths in integer unless you absolutely insist on introducing floats. Integers are 32 bits. Variables can be up to 31 characters long. There are three types, using % $ and # for real as the last character, and the default can be anything you want (realistically most work is done in Integers - if you use float variables it has to convert it to/from float for storage). It is a little, but not significantly quicker than MS Basic, unsurprisingly, because it's largely doing the same thing. A = A + 1 involves much the same binary manipulation. I've started on command words (other than LET, RUN etc.). Including GOTO. You just won't need GOTO.
M65 is much quicker, of course, and I haven't made any 4510 specific optimisations yet, though the framework is all there. In FP math for example there's a lot of mantissa shifting going on, which on a 6502 takes four seperate instructions, and a 65816 two. The M65 does it in one instruction
No specific losses. One limitation is data. Program Data is limited to a 64k block (the actual program can fill the whole memory space anywhere). However, the plan is that this is only actual variables ; things like tiles, graphics and sound are kept elsewhere.