I have no idea. I believe they will start realizing that click-based advertisement is an increasingly unsustainable and flawed revenue model and will look for a ways to start a significant portion of revenue from another source. Assuming that:
1) They don't have time to build it.
2) Since, they will need to buy it, it should be a business that already generates significant revenue, thus the biggest acquisition price tag
3) The longer they stick to click-based ad revenue the lower their chances to diversify and the higher the chance that someone else comes forward with a new revenue model that will irreversibly undermine Google's.
but to be a biggest acquisition, it has to be a few years old unicorn with a solid revenue models at this point. And among the current ones, I can't think of any that would give Google an opportunity to diversify from their click-based ad revenue. Until they do something radical and acquire robinhood or coinbase.
Actually, Stripe is a really good one. Shopify, I dunno, I can't see it meshing too well with Google's current products or google even doing a good job developing Shopify further, especially after being acquired at more than 100B$ valuation. But a Stripe acquisition, I think, will be mutually profitable.
* A security breach bigger than SolarWinds will be discovered and will severely affect market position of a major cloud provider
* Google will make its biggest acquisition ever
* Inequality, censorship, and polarization will continue to increase