There's 1% possibility that the other 70 will debut in the future sister games of Pokemon XY. As for the compatibility concerns with XY, either there's a patch to allow trading, or simple blocking new Pokemon to be traded like Time Capsule in GS series.
I sorta understand where is that Level 70-evolution coming from, because the E4 in Kalos are high leveled! {D:}
Think of this as this way -- If you have Goomy in your party, it shoulda evolve by the time you reach E4. :)
I admit that evolving at Lv.70 creates a little problem for post-game training. In fact I kinda lost my interest to level up my Zweilous in BW1, gladly Join Avenue was introduced in the sequels, things went easier for a bit. So let's just hope for a Join Avenue or similar features in XY! ;)
I can imagine frilled dragons as the pseudo legend! I have no idea for the Fire starter tho, and there should be a better candidate than platypus as the Water-starter (Don't take it that way! I love these amazing creatures)!