One change I think they should make is that certain LIs should be unavailable if your character is their polar opposite. Alien squadmates shouldn't be interested in a protagonist whose views are aligned with the Terra Firma party, for example. Also consistently using harsh renedouche dialogue with potential LIs should close off the romance path.
Well, not all of them. I can see certain characters responding better to "tough love" way of romancing. Of course, renegade doesn't really lend itself well to any kind of love(or at least it seems like that to me), but if they do the morality a little different in the next game(maybe classic good/evil system would work well for that), I can see some characters responding better to the "negative" axis and some better to the "positive" one.
Making everybody romanceable just by paragons is just as bad as people staying with Shepard if he treats them like dirt.
I don't have a problem with the asari in this regard because being a monogendered species who can have mind sex with any other being they want, is their whole niche. That's their thing.
That doesn't mean Bioware should've went all ME2 on us and said: "Quarian, Drell, Turian, bang 'em all". Just to make everybody happy. Fan service at its worst. A detriment to creativity. It's hard to take seriously at all.
Just you wait and see, next one is going to have a hanar squadmate. And yes, they will be romanceable.
For my part, I'd like to see some tough choices included. Include a chance for your LI to die, but make it optional. Sacrifice them, or your other squadmate. And when/if that happens, have the rest of your friends and environment in general comment on it. Or make something bad happen to them, but have a chance of reversing it. The mission in BG:SoA, where Bodhi captures your lover and turns them into vampire, forcing you to kill them comes to mind. I'd love to see something like that.