Even if reimbursement goes down, the specimens aren't going to go away. Compensation would go down, which based on normal human behavior would mean fewer people would go into these fields. I would not base your career decisions on what the "hot" fields are currently or what you think they might be. That is a setup for landing yourself in a career you don't like which becomes doubly unpleasant if the "hotness" doesn't materialize like you thought. The "hottest" fellowship is the one where a resident learns to communicate and not to be an arrogant ****. But those fellowships are rarely completed.
I don't know any unemployed GI fellows. I'm sure path24 does. Some had to travel a bit to get a job that had the characteristics they wanted, like only doing GI path. I'm sure some took jobs that others wouldn't take like working for an in office lab or a reference lab. But there are a lot of GI path reference labs out there. The job market is much better, from what I hear, for GI fellows who train at good academic centers, than for those who do a "fellowship" at a reference lab.