The day after my birthday like a fashionably late present, Chasm is to launch with same-day Linux support on July 31st.

You can't link directly to comments on Steam news posts, but the developer clearly replied to a user asking about Linux support with "Win/Mac/Linux on launch!". You can't get better than that!

They also released a new teaser:

Features:

Explore six massive procedurally-assembled areas from hand-crafted rooms

Enjoy challenging retro gameplay and authentic pixel art (384x216 native res.)

Battle massive bosses and discover new abilities to reach previously inaccessible areas

Customize your character by equipping armor, weapons, and spells

Linux, Mac & Windows versions with full Gamepad support

I've been personally pouring hours into Dead Cells and it's completely hooked me in, so I very much look forward to another experience like it. The teaser trailer certainly does a good job of selling it to me, that cute deadly little creature at the end was brilliant.

You can read their announcement about it here.