Yep yep. An appendix of variant rules -- with discussion about their implications, both in isolation and combination -- will add a lot of value.What I'm saying is that I'd put capstones as an appendix.
Is what I'm saying. So that way people get whatever flavor they want.
Agreed about keeping out monsters whose spell lists cause them to be "too high" - give them another appendix.
I'm going on the record agreeing with this. There's no need. It was something I introduced because a lot of people wanted it. I'd rather a "core E6 rulebook" didn't have anything except the base rules to level 6 (but picking base rules is up to you folks)
I don't see the point in having the stats for a tarrasque. The PCs can't do anything about it, so it does whatever damage the DM wants and leaves. Even the rest of the creatures need thought; if humans can no longer reach 15th level, real powerful intelligent creatures either need to be running things or have a good reason they aren't.
E6 talks about the characters in a realistic sense. Read The Alexandrian. This is the entire reason for having E6. If you don't get into that headspace, none of the creatures make sense. E6 is about scale, getting away from the unrealistic ability of a character to not die horribly after being stabbed properly.
The point isn't always to have monsters the PCs can beat. Sometimes it's more about knowing what a creature could do if it were there. Having the stats of the horrible thing that the BBEG will release if the PCs don't win.
Terrasque notwithstanding, the PCs could run across an area with a giant Dragon in it.
I understand that, I think. But in most TSR worlds, humans are the apex predators. Nothing is going to march straight into Waterdeep because humans will stomp it into the ground. In a E6 world, if there's much big nasty stuff around, why isn't it running Waterdeep or has destroyed Waterdeep?
Er, an Adult Red Dragon (from Pathfinder) can basically autokill any 6th level character with its breath, force them to make DC 21 Will save not to run away (i.e. a 6th level cleric might bring that tp 50/50), has a 29 AC, DR 5/magic = actually hurting it is going to be extremely rare, and 212 hp = even if you can hurt it, it's not going to make a difference. And Speed 40 / 200 flying, so even if you can make a plan, it can outfly it. What more do you need on stats? This is a tarrasque--completely unkillable short of a wish--in a E6 world. If it shows up, you're either going to try and engage in diplomacy, run away, or use the Macguffin against it. Go ahead and wing it; the stats just don't matter.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.