The thing that tipped my belief over into Coinbase adding Monero soon^TM was actually Kraken's adding it last January.

Seems to me that both companies are probably pretty competitive, both being USA-based Silicon Valley crypto startups: whatever one does to 'lead' the other will want to 'follow suit' at least just to maintain feature compatibility.

If Kraken had added Dash only, Coinbase couldn't really only add Dash too since Monero is clearly the more advanced tech.  In this case, they'd have to add Monero to look smarter, LOL.  By contrast since Kraken added Monero *first* now already... if Coinbase 'matches' now by only adding DASH...?  They'll kind of look like idiots  

So IMHO looks like Coinbase has to add at least just Monero now, or maybe to one-up Kraken they could raise the bar and ADD BOTH MONERO AND DASH SIMULTANEOUSLY!!