The proposal is reasonable on paper but unrealistic in terms of grounds for execution.
The benefits are too small for Anime.SE - which already banned this type of questions after having dealt with them for long enough to identify it as problematic - to be worth the effort.
The questions in concern are not dire for migration - If a question is closed but meets the standards for Sci-Fi, the question askers can already be manually redirected as-is.
Handling identification requests to decide if they're worth migrating shouldn't be the problem of that of our moderators and/or reviewers. However, the linked discussion thread on Sci-Fi.Meta.SE includes the following points:
Anime's own users and mods will do some quality control for us, ensuring that inappropriate questions (such as those that don't contain any SFF content) won't get migrated over.
We've had a TON of migration discussions on SO, and they inevitably break down because the target site gets a lot of rejected migrations. Invariably, what will happen is it will promote the lowest common denominator. "Oh, a story ID question. Off to SFF you go!", only to have us now do more work to close the ones not in the rules.
if ID questions are getting closed over there that would be upvoted and answered over here, then there's no reason not to deprive those questions' OPs of getting their answers.
These quotes outline the two main problems behind the migration option:
It is an idealistic implementation with the hopes that our users can identify questions that are worth Sci-Fi.SE's users' time. However the last major thing we have been able to decide is that they aren't worth our own time (even after trying to improve and fix them), so our users are not likely to re-learn a new set of quality guidelines for identification questions that we've already tried before and has in no way worked out, not barely.
This generates unnecessary work as a side effect. Where as currently "identification questions are off-topic, because they tend to attract low-quality and low-effort posts", the proposal has not addressed the problems (why do you want floods of low-quality and/or low-effort posts?) (edit: have not appeared to discuss in regards to remedying the problems to be worth the effort) and wants our questions that are fantasy-related. This leads to every new identification request having to be scanned for fantasy, it's not a trivial amount of work for a pool of questions that Sci-Fi users have no promise to fix into shape.
Conclusion: Implementing the migration path appears to be a liability, and as there is no compromise to be made, it doesn't seem like a good solution. However, as with all solutions, they should be implemented to solve a problem. While a migration path is not a good solution, there may exist others when the problem is identified.
Identification questions has made up a large percentage of our regular "income" before they were banned, so there is definitely a "market" there but there needs to be more realistic ways to get questions over to Sci-Fi (while taking into account that we want all of them out of here without worrying about fine grains).
I can't imagine that Sci-Fi isn't already getting its fair share of animated fantasy works and the existing field there is healthy. Implementing this migration path without solid promise for their users to be doing the work to fix them into shape would only pollute this small haven and waste both of our communities' time.
Addendum: Recently, some users (should this even be plural? I didn't notice if they were the same persons) have been manually redirecting question askers for the possibility of reposting their question there. You can judge the results for yourself.
Post script: I didn't realize what a migration path meant, I assumed the discussion was surrounding opening a new close vote option for all reviewers. While I think that good questions that could find a home on Sci-Fi.SE safely may be worth migrating to on a case to case basis, it shouldn't be Anime.SE's job to identify them.
Post-post script: I was right in assuming what a migration path meant, ignore this block. As things are now, manual migration by moderators is already possible.