1.First of all, you can daisy chain MegaDrums even today, and you can configure them manually for 64 inputs. It is just that it won't be possible to control them from a PC when they're daisy chained.
2. I didn't say I wouldn't add SysEx support for daisy chained MegaDrums. It is just of low priority right now due to little real interest in it.
3. MegaDrum may be capable to support 64 inputs in one module. Again it is of low priority due to little real interest in it.
4. Other projects/products with 64 inputs?
E-drum, Roland, Yamaha, Alesis? Maybe in fact it doesn't have real demand?