Developing an effective jailbreak is an extremely complex and challenging process. Only a handful of talented individuals do it. 4.3.5 represents the end-of-line for the 4.x firmwares , so there is little motivation for folks to concentrate on it. IOS5 will be out next month, and it is likely that those who are inclined to develop a JB will be concentrating on that...
The only way 4.3.5 is likely to get a JB is if an exploit is found in the future which works for both 5.x and 4.x, or if an effective bootrom iPad2 exploit is found (which at the moment, it has not). 4.3.5 can be jailbroken (tethered) for the iPad1 because we have a bootrom exploit for the A4 chip in it. It is only the iPad2 and its A5 which is a real challenge today.
Furthermore, Apple has significantly tightened the SHSH security on IOS5, so the golden age of jailbreaking may be now, as the future could be quite a challenge. Certainly the days of being able to restore and rejailbreak at will if you have prepared correctly will be long gone with IOS5 firmwares.