I don't think it have sense because it is the same png format. Most (99%) programs that can show you one will be able to show you another and png is old format so converting from one to another format is supported in 99% drawing programs. I recommended the indexed format because it just save space by using 1 byte per pixel instead of 3 or 4 for rgb or rgba. I don't think that providing only indexed version will hurt anyone, at least it is what I usually do for my packs