Well what do you suggest replacing "clothes, etiquette, and other things" with?
There are differences in these from organization to organization in Aikido...
Aikidoka's reduces hakama, start to do sparring and becomes sambo
It's near by self-definition as for me. If you take all ideas so you will be aikido guy but if you ask: "Why I had to bow this old man photo?" you need something different. Maybe the motto of japanese martial arts is: "All or nothing".
Yesterday, I was in the park, training aikido weapons with friends from several different aikido clubs. There was no dojo. We were in shoes and on hard ground, so there was no seiza. There was no kamiza with a picture of O Sensei to bow to or raise our weapons to. We did not wear gis or hakamas. Were we still training aikido, or had we invented something else?