In a recent AMA on Reddit, lead writer on the first two Mass Effect games Drew Karpyshyn expressed surprise at people getting horny for Garrus.
An important thing to consider when writing a story of any kind, is that if you make any kind of humanoid race that can bone, people will want to bone it. Characters like Garrus might not be to your taste, but plenty of people would happily bend over backwards for the turian, much to Karpyshyn's surprise.
"We always knew they'd come back as companions," wrote Karpyshyn in the AMA when asked about how Garrus and Tali were brought in as romance options for Mass Effect 2. "I was a bit surprised fans wanted the romance options. Tali I could sort of see... you never saw her face, so it was easy to imagine something vaguely human. (But she had those weird feet!) Garrus blindsided me—but once we saw what fans wanted, we decided to deliver!"
Garrus is a notable fan favourite of the series, so anyone in the know could obviously see why he should be a romanceable character. Though unfortunately for those that pictured having a loving family with him, that probably isn't on the table.
"The various species in Mass Effect are too biologically different to breed with each other," wrote Karpyshyn. "Except Asari, of course... it's part of what made them unique. But that's just my personal take; I don't work on the series anymore so if BioWare wants to have Turi-quar babies, that's their choice."
While the former Mass Effect writer does note he's not on the series anymore, BioWare probably will take the safer route of not allowing you to have babies with another species.
But who knows? A new Mass Effect is on the way, one that might see the return of the Geth, so anything could happen.