Some sources update faster than others, you could index news sources hourly and low velocity sites weekly. Google does that. CommonCrawl gets 7TB/month, indexing and vectorizing that is quite manageable.
Running an index is an extremely profitable business, from multiple points of view (you can literally earn money, but also run ads, you get information you can sell, you can buy mindshare). Everybody is looking for indexes beyond Google and Bing, but there are none. If it really is as easy as indexing common crawl, then I think we'd have more indexes.