According to the blog post, It will be possible to unlock the boot loader for certain releases of SE 2011 Xperia phones, such as Xperia arc, Xperia neo, Xperia pro and Xperia PLAY. This will be limited to only sim-unlocked phones, so carrier-partnered versions are out of luck here.
Well, get ready for flurry of cool custom ROMs.

One reply on “Sony Ericsson wants to be dev-friendly; will let you unlock boot loaders”
Will most likely still void your warranty.
I would much rather see and option to install a “stock Android” version without voiding the warranty.