Well this is way above my pay grade so I am only assuming here...
I think Spiber needs to wait the generations as well but because they are using ecoli those generations pass in a very short time. I imagine they also go through a selective "breeding" to produce the ecoli that is expressing the traits they want the most.
If they have a way to put any protein gene they want into an ecoli and have that protein expressed in goo they are on to something. The silk protein powder mixed with protein X powder then spun into a fiber could find a lot of uses but I think just the protein factory itself would be a better business.
This tells me they can not just produce any protein they want at will. They might be able to do it in the future with a different bacteria but they are restricted to smaller genes right now.
I can only fall back to something I have said before.
There is no way to be cheaper than a silkworm when you need a silkworm to begin with
I do think that the people working with protein goo are really fascinating but unless your end product is the protein the spinning process for silk is too costly to compete with a silkworm.
As you say we will have to wait and see. In a few years the hindsight will make things obvious.