Look no further than Photozone, Joachim. 
http://www.opticallimits.com/canon_eos_f...f4556eosff
Looks like this lens was discontinued in the interim - so that's one more reason to expect a successor. Whether this new 100-400 is one remains to be seen.
Re: the 135/1.8 filter threads - there have been some such lenses with 77mm filters (most importantly, the fabulous Zeiss ZA). However, 82mm is the new 77mm anyway.
http://pp.vk.me/c636322/v636322358/47f6b...8guRM4.jpg
http://www.opticallimits.com/canon_eos_f...f4556eosff
Looks like this lens was discontinued in the interim - so that's one more reason to expect a successor. Whether this new 100-400 is one remains to be seen.
Re: the 135/1.8 filter threads - there have been some such lenses with 77mm filters (most importantly, the fabulous Zeiss ZA). However, 82mm is the new 77mm anyway.
http://pp.vk.me/c636322/v636322358/47f6b...8guRM4.jpg