There is certainly precedent for the WT to eliminate the blood doctrine. Note how they accomplished something very similar with respects to vaccination:
Questions From Readers
“Is vaccination a violation of God’s law forbidding the taking of blood into the system? – G. C., North Carolina.
The matter of vaccination is one for the individual that has to face it to decide for himself….our Society cannot afford to be drawn into the affair legally or take the responsibility for the way the case turns out….all objection to vaccination on Scriptural grounds seems to be lacking….We merely offer the above information on request, but can assume no responsibility for the decision and course the reader may take.”
– The Watchtower 12/15/1952 p. 764
It can be safely assumed that JWs who skipped vaccinations for their children suffered the effects of polio, measles, mumps, rubella, etc. My suspicion is that most JWs continued to feel that vaccinations were a contamination and avoided them whenever possible. That attitude persisted among JWs for decades and I remember it well. We would likely see something similar with blood.