Add project filter on import

I understand this choice, but here's our situation :
French community has raised its level of translation moderation since this summer to take down the 10.000+ suggestions we had on the projects (we are at 6300+ so far). The fact is that we are too quick for our contributors who are not all using l10n_update to keep their localized installs up to date. So when a user who does not have up-to-date locales import a full .po file of his site, with the intentions of only translate a project, his old locales are re-inserted in the system as new suggestions, making our work endless.
I understand your point, but please consider ours ;)

Another thing that could prevent this behavior is to add a step between the user import and the real insertion in database : a sort of import validation, of course this validation would be optional, perhaps on a group-level?

Also, the project filter I was talking about would be optional too...
Cross-pollination would still happen as the translation are not on a project level but on a string level. The only case of losing translations is if an imported translation doesn't exist in project filtered, but does exists in another project.