uhm... how do you mean writing is fast and reading is slow? reading is always possible faster than writing. if writing a dvd in 15 minutes is ok for you, why is reading it in 15 mins too slow for you?
if you're getting slower reading speeds, you most probably have a misconfigured system. your HDD isn't using UDMA or somesuch...
also remember that the most common use of all these optical discs will be just for watching video. anything as slow as 4x speed is plenty for this purpose (i guess theoretically 1x should be enough) and the technology is expected to get up to 12x at the same disk rotation speed used in current DVDs.
also any tricks for speeding up reading, like using multiple lasers and such, arent a topic of the actual BluRay format specification - they're up to the drive manufacturer. if there is need for it, be sure it'll be implemented.
btw 20 beams sounds too excess, to the point of being ridiculous. the details of actually producing such a drive aside, 20 beams each reading at 12x will result in 240x read speed, i.e. more than 120MB/s! There's no HDD out there that can manage a sustained write speed like that
EDIT: ok my MB/s figure might be off... hmm, I'm too lazy to search for 100% true info, but it seems it might just as well be 240MB/s
Also if you think about it, a single laser can read mutliple layers at once, which will speed things up the same way as if there were several lasers (if data is properly interleaved between the layers). With the expected 8 layer disks I dont expect anyone could find the reading speed too slow