Are there any plans to offer a Relax NG format of the Collada schema?
A lot of the XML tools these days are 50/50 split between XSD and RNG validation (a few support both).
We have no plans to translate the schema to other schema languages like Relax NG or DTD.
What tool do you want to use that does not import XSD?
Nothing specific.
A lot of the existing projects that offered only XSD schemas have been adding RNG support as well lately and I was curious if Collada was likely to follow suit.
The primary advantage for me is the ability to convert into of Relax NG compressed format for readability reasons.
I do not currently know of a conversion path that can go from XSD -> RNC. Although conversion from RNG -> RNC, RNG -> XSD, and RNG -> DTD is pretty mature these days.