We can confirm, that a successful 3.55 downgrade method has now been released. We previously reported on KaKaRoTo's attempt to provide a 3.55 downgrade method. However, the inability to reproduce his results, ended up roadblocking his work. This time around, solidpsycho, of PSX-Scene is claiming to be successful. He released a modified 3.41 PUP which we have personally tested, and can confirm its legitimacey.
NOW ONTO THE BAD NEWS
There are reports of this bricking Slim consoles, do not attempt to downgrade a Slim console with this method. Older Fat PS3's are reporting no issues. Also, after downgrading to 3.41 with this method, your PS3 will think its a 3.56 console. Once on 3.41 it is recommended that you then downgrade the traditional way to 3.15 firmware, and then upgrade the traditional way to 3.41 official firmware.
Update: Unconfirmed - slims with firmware version 3.41 or below from factory will downgrade fine.