yes i did not propose a double end bag because that's not geared to condition for evasion and for dancing around but for hitting which aikidokas don't need and arguably don't even want to do
Those bags are standard in boxing but are used to condition you to HIT a mobile target not really to evade it besides with double end bags you can evade straight punches but you will never dodge to evade hooks
The best would be a short bag like here at 00.48 http://www.youtube.com/watch?v=EUDogb3zO0U
but do not just evade also dance around abundantly for in a real situation you will need to take away the distance frequently unless you're fighting inside a phone boot lol
Most scenarios won't have much space but will have some although in a bar you may trip on stuff fallen around when people panic and begin leaving the place in a disordered rush as you're left there to mind business alone and security may take a while at times to take over
I've found the double end bag very useful for evasion. Hang it a little high (which is a good idea anyway, condition yourself to punch up), put enough tension on it so that it bounces around quickly, but not so much that it doesn't have a couple feet travel if properly smacked, get in close and give it a stiff jab. Just use weight transfer and upper body evasion to avoid getting hit by the return.
But, fights dont always go down like you describe, and we cant train for every situation. It isn't punching, squaring off and floating like a butterfly that wears someone out in a fight. It is fear, having to maintain a heightened sense of awareness, and having to deal with a ginormous adrenaline dump. The only fight I was actually in (meaning that the attacker had engaged me directly rather than me intervening in other folks fights) doing security lasted about 45 seconds, did not involve me moving anything but taking one step into a hanmi and flapping my jaw as I talked the guy down, ended perfectly well, and left my entire body sore for three days.
I think it is better to work on psychological self control and dealing with physiological fear responses than dealing with overly specific defense techniques. If self-defense is what we're training for (and it is fine with me if it isn't) than we would do well to work on the non-physical as much if not more than on the physical. That training has been lacking, at least on an upfront, explicit level in every dojo I've trained in.
To tie it back into aikido, if only loosely, take an On Guard class from Kevin Blok sensei if you get a chance. He will at some point in the class talk about the mindset most likely to get a person home for dinner. Comes across like pirates and ninjas and zombies and Neil DeGrasse Tyson and everything cool and worth watching doing the St Crispin's Day speech from Henry V. You KNOW he's been there, done that, got the tshirt, and is telling you your real business.
The other side of the real fight training question is this... If aikido is a budo of love and harmony, how many dojos provide training in mediation, de-escalation, and communication? Mine doesn't, and I wish it did.
This is a bit more of what it looks like, in my experience. Rambling, skill-less, back and forth, lots of useless folks getting in the way and making things worse, jawingjawingjawing, most likely drunk....