I doubt they will ever be cheap because they will never reach an economy of scale.
Not many people will really want to convert vinyl to digital.
Most recordings that most people would want are already available digitally and at a much better quality than could be achieved by converting a vinyl record to digital.
Pretty much a special use item for museums and professional archivist.
That's true. For folks with large collections of LPs though, they could be a lifesaver. I can easily understand hard-core vynal owners shelling out bucks for something that won't wear the record when it is played (as even the best needles do). With modern DSP equipment to remove the inevitable pop and click, it might extend the live of LPs for quite a while.
My wife's uncle Bob had (conservatively) 10K albums when he died. He'd started converting a bunch of them to CDs in his later years before he passed, but didn't really make a dent in his collection. Someone really got quite a haul of big-band, blues, and old country stuff when his estate went up for sale. Unfortunately, family issues kept us from actively trying to preserve it.
The last few years we would take a paper bag full of CDs from him, take them home and rip them, and hand him his disks back and a couple of DVDs to load on his computer. He thought it was better than sliced bread because he had so much stuff available right at his fingertips. Of course we kept copies so I have some really interesting stuff in my collection. I have a copy of "Rising Son Blues" recorded in the late 30's to early 40s. It's the oldest version I've ever heard of what became a big hit with the Animals as "The House of the Rising Sun".