The FCC just voted to reclassify broadband under Title II of the communications act. Could this be used by a new ISP (like Google) to make use of existing ISPs cable infrastructure (e.g. Comcast's cable)?
In theory, it could happen in the future, but not under the current order.
We don't have the full text of the order yet, due to the internal delay for the FCC to prepare it (The Nay votes get to write opposed opinions, then the Aye votes need to write a counter to explain why they didn't think the opposing reasons were valid enough to change their vote, then it gets a final vote of approval from everyone), but from statements that have been made about it before and since, the FCC has chosen to "forbear" from enforcing that line sharing.
This article quotes an interview where FCC Chairman Wheeler said:
There are 48 sections in Title II. In the wireless environment, the FCC forbeared from, did not use, 19 of those 48. We're not using 27 of those [for broadband].
I don't have the specific list, but I do know that line sharing is one of the 27 that aren't being used. Google actually asked the FCC to include it, back in January (before the vote), but didn't get it.
I would assume the process to change what rules are forebeared from would be just as involved as that of reclassifying them as common carriers in the first place, so it's not likely to happen any time soon. But this article (which is a great explanation of how forbearance came to be a thing) says that "unforebearing" has never really been tried, so who knows?