how many would like to see a delay for the 500 frame?
what kind of delay times would you want to see.
i am thinking 500 mil-secs, or may-be a sec.
i am thinking primarily for pre-delay but all info is want ~
i think fet, or would the world want transformer coupled?
delay and buy-pass.

hard to say...one thing about delays is they are (at least to me) continuously adjusted during the course of a songmix...pretty touch to do this when the device is in a preamp rack or chassis somewhere well out of hand.

But to answer your question as asked: it should be designed to have several varying ranges...much like a Boss DD3 pedal (which is what I use 80% of the time)...

To my ears, nothing sounds as absolutely perfect as a tape driven Echoplex (or similar) in almost (not perfect, but almost) perfect tempo .... with each subsequent repeat rolling off a little more high end than the previous echo...

And of course, have the stereo/mono option

it would be nice to get quality so as to use it for pre-delay yet have the versatility offered by more delay time.
i keep looking at ebay hoping to score a monster deal on something like the older Lexicons.
it just seems they are getting snatch up at a somewhat high price.
i think a 500 frame delay could be more affordable possibly?

I think part of the appeal of the PCM-42 is the user interface--easy to get into all the functions. The Delta Labs delays sound good, but also benefit from a good front panel--that package with a cheap used price and it's no wonder folks are nuts for them. In a 500 rack, you can only do so much with the real estate before you have unfriendly control complexity. I'd say keep the control simple, then, which probably suggests simple function.

Bear

i think something simple and just to do the job.
to get much delay the digital may have to come to play, in order to maintain quality of sound in the upper frequency range?
i would like the added delay time as it would make for a much more versatile delay, but i could also be happy with some just for pre-delay.

The 500 format is mono, right? Unless you're going two space, I would say go with a high-quality analog bucket-brigade type delay, as long as is practical, with a nice old-school set of analog circuitry--discrete, transformer balanced. I think that would be unique on the market.

If you want complexity, look at a 2-slot stereo format so you get some panel space.

Bear

yes you are correct : )~ The 500 format is mono.
two slots is not uncommon with-in the constraints of the 500 format, although i prefer a single slot, at times it simply is not practical.
for example my buzz audio essence comps are two slot and take advantage of the second slot for side chain and linking.
for this i have no issues giving up the second slot.
if a delay were to have some versatility again, i would not look at it has loosing a slot, but instead, gaining more versatility, at a slots expense.