for me, the artist who's really doing best with gradually evolving his sound while also maturing a signature sound is Alio Die.
The current best ambient musician in the universe IMO!!!
He's been releasing some amazing little soundworlds- well some are little and others more grandiose, but he keeps impressing me big time. And I'm not a fan of his stuff that's too experimental- the ones with "noisy nature" ambience or too much in the abstract, but lately his works one after the other have been intriguing and at times just gorgeous.
Of Steve Roach's last 5 years or so of output, the ones that have appealed to me are Sigh of Ages which is uniquely somewhere in the middle of austerity and warmth. Back to Life is pretty good, and the Delicate Forever has Steve capturing some of the signature minimalist "magic" that we've come to know & love, at least in that first and last track.... and for collaborations I've enjoyed the Road Eternal w/ Eric Wollo & The Long Night w/ Kelly David.
Oh, and the latest and once free download "Invisible" is a straight old school Roach album that's gotten some good plays, reminiscent of the slower atmospheric buildups in the Origins/Artifacts era- it's vintage stuff without feeling rehashed, it seems....