This is a really useful discussion and there's a powerful idea. I agree with Ravi that there is an opportunity to build awareness and traffic to Indic language sites. While we are already seeing considerable readership of Indic languages, there's clearly a lot more that can be done to support this and also to help build Indic language communities. I also hear Theo's point that it didn't work last time, or maybe wasn't adequately measured.
I'd like to suggest that - even as the technical challenges are resolved - to explore this. The first step would be finalise what the objectives are (e.g., is it basic awareness building of the existence of Indic language projects or to is it to drive readership of these projects or is it encourage more active participation in these proejcts?) The next stage would be to test different banner/notice/page design options and figure out the most appropriate solution (in the same systematic way that the WMF fundraising team tests banners and optimises the ones that work best.) If you see value and you think we need resources for this, I'm happy to see what we can do about it. (Maybe see if any of the fundraising team's people are free after the fundraiser to help with the analytics for determining what might work best?)