The "Generation" change didn't really solve anything and created a whole host of new problems.
1. The identification of the "Great Crowd" in 1935 is still inseparably tied to the old generation teaching.
(i.e. Since the great crowd survive the great tribulation, it must, of necessity occur within the lifetime of anyone alleged to be of this group. Consequently, JW's currently believe that there was only one hope, the heavenly one, from Pentecost clear up until the proximity of the end made the identification of the great crowd possible. )
2. Modifying #1 above would create a third class of Christians that the JW's are not prepared to account for.
(i.e. The JW's base their two class salvific system on their unique interpretation of John's temple vision. John "saw" only two groups. This is why the JW terms, "Other Sheep" and "Great Crowd" are completely synonymous in the Christian Era )
3. Modifying either #1 or #2 above robs a life spent as a JW of any meaning.
(i.e. In practical terms, what would be the difference now between a JW with the "earthly hope" that died in a concentration camp and an SS guard in that same camp, now that they are both dead and awaiting resurrection?)