When I was doing some research before I bought my dot, Sonos have been promising compatibility for many many months, seems to be a bit like the last GOT book, always promised but doesn't materialise.
I almost bought an echo on prime day but after reading reviews on the echo speaker I decided on a dot and a bose speaker - links up easily and sound is fantastic - basically a dot is an echo without the big speaker. The dot still has a speaker but its pretty poor quality to listen to music on.