I can’t help but notice that the Kosmo format seems very lacking in the area of reverb. Just about everything seems to be a variation of a spring, pt2399, or accutronics brick circuit.
Right now I’m piping things through pedals or eurorack, but I sure would love to find out how/if others have solved this problem within their Kosmo rack.
I have a Music Thing Modular spring reverb behind a Kosmo panel. Perhaps the new Sound Semiconductor BBD could be a cool option as well for shorter times.
If “deep ambient” implies longer reverb times, the only options are either physically large electromechanical devices (think reverb plates) or DSP modules. Both are challenging in their own ways, and the cost of materials (sheet metal or a Raspberry Pi) will likely surpass the cost of second hand rack units or effects pedals, so I am not surprised that we haven’t seen much beyond spring and “Brick”/PT2399 modules.
Having said that, I could imagine that one could come up with a Kosmo module based on the cheap “100 different DSP effects” module that you could find in the usual places online. Some variation of a typical amplification/mix/feedback circuit around that module, with a couple of VCAs for voltage control could get you there.
i really mean more along the lines of the complex digital reverb algorithms found in pedals/eurorack. For example, there are several very good reverb pedals based on Teensy or Seeed that I’m surprised we haven’t seen migrate over here.
Like the funbox for example: GitHub - GuitarML/FunBox: Stereo guitar pedal platform using Daisy Seed.
Right! I Here is another Daisy Seed reverb project I am aware of.
I think one problem with these projects is that they require boards that are not widely available (like an Arduino), or they go out of production after a few years making the associated projects obsolete. For instance, I don’t think you can find Daisy Seed in many European countries, and you cannot find Teensy 3.* anywhere any more. If you find them, the cost to have them shipped and assemble a module might be possibly similar to a used Lexicon rack unit 
I know the UK did a very silly thing but Thonk is an excellent source of kit this side of the Atlantic. Not EU, but not dealing the Orange Menace’s tariff nonsense.
From Thonk I bought a Ksoloti Core, which is the successor to Axoloti and can do some absolutely amazing reverberations. I’m not a Kosmo builder because I like 3.5mm jacks but my Axoloti build includes a faithful version of Mutable Instrument’s Clouds which I will happily tweak for hours. (Chia and Bran modules here.)
Ksoloti is brilliant, highly recommended. Great hardware and software and some very clever people on its forum.
(They frequently have Daisy hardware as well, but I’ve found Ksoloti much more fun!)
Sadly the UK had their own idiotic trade policy with Brexit which means shipping+VAT+import taxes+import processing fee. Not really worth it when the price in doubled at the checkout and nearly tripled when it arrives.
Oof. The only “winners” have been the leaders of the far right 
On the upside, the gold toilet market is BOOMING lately.
