Lots of good stuff said already so I'll just add my votes.
--2 way minimum, we need that tweeter.
--AC vs. battery?? as long as it's not battery only. Question... How long can a decent speaker last on a set of batteries anyways?
--Left and rights are separate units. I have never understood stereo when the two speakers are mashed close together in a single unit. Two channels give better sonic reproduction I'm sure but certainly no stereophonic effect.
--DLNA would be useful, but I think this would overcomplicate your product. You are not trying to build the smarts into the speaker, you just want to make it an audio slave (no reference to the band intended) to other smart devices, correct?
For me personally, if I was buying 'outdoor' speakers, I'd go with permanent outdoor speakers. For this model, an indoor set that I can occasionally drag outdoors would be fine. I'll pull em back in if it rains.
--Don't shoot me folks but if you go with an outdoors model, they may need a bit of a bass bump to overcome the tinney outdoor sound some speakers get without reflection points, but hey, I'm delving into design here, which is your bag and I know nothing.....notttinggggg.
With great power comes Awesome irresponsibility.