1) Someone invented Tor2web, therefore someone else is likely to want to reimplement it; ideas tend to persist in this way

2) (as observed above) Google *do* crawl onion sites via "onion.to", which is a fun surprise for people who insist that "The Dark Web Is Not Indexed And Is Therefore Spooky"

3) Making such a move to block Tor2web-like sites might engender false trust amongst the people who set up Onion sites: "It's Okay, Google Can't Get At Us"

I would recommend investing more effort in Tor2web/similar, because having a permeable barrier between IP-Space and OnionSpace appears useful.

At very most I might propose that:

a) OnionSites become aware of the X-Tor2web header which (from legit T2W instances, at least) permits the OnionSite operator to block or redirect the user to use a "proper" Onion network connection

b) That TheTorProject consider indexing known Tor2web sites and publish them, perhaps adding a feature to optionally block them from TorBrowser access**, thereby to prevent stupid intra-Tor deanonymisation loops

    - a

*although speaking as a geek I believe that re-engineering T2W to support SSL via SNI-Sniffing would address this, it would be a gross and pointless hack, complicated still further by certificate issuance, and all reasonable use cases for which would be better addressed by running a local copy of Tor.

**the hardcore alternative of blocking them from being accessed by exit nodes causing a likely-intolerable argument.