Very reasonable, they can create their own bitcoins by keeping Bitcoin safe.
Unlikely to happen. The mining procedure making anybody trying to mint their own coins useless. The quantum computing was another scare tactic, nothing more.
In the long run they will have to develop one of their currencies. If they exploit all the bitcoins in the market and sell them, the liquidity will be zero. They will not be foolish to destroy this market. There are many people who own bitcoin and the majority are their customers and partners.
Seriously speaking, a tech company like Google would never go into that direction. They are nonethical enough to save your data but ethical enough to not sell it, similarly their owners are rich enough to not make any attempt to ruin the market. They have much better uses of quantum computing than to attempt to destroy something which has a good use.
However they may create their own altcoin and promote its usage for paying, maybe google pay use?