Makes it hard to follow who said what in threaded mailers. Right, that's why I never pushed the rewrite it in Scheme issue, which is what I'd like best. And I fully understand the functionality issue. That's why I'm arguing in favor of some sort of focusing of effort. WRT reports, even if it means initially leaving some of that code in perl and internally dumping the output from xacc into the scripts as text, then that's probably not a big deal.
Splits are absolutely essential.
This is something I have experience with. Note that the current CBB alpha has some support for this, but the interface there still needs some work too. That was top of my list. If I'm involved and not muzzled, that'll be possible. I wasn't claiming that it had to be slower.