Yes, the protocol is designed to be extended with different AMMs.
Yes, the Liquidity Reserve and Insurance Fund are shared by all AMMs.
In Perpetual Futures Swap, there are several events that might cause losses from the stakers:
Negative Funding Rate
The positions that AMM hold would need to pay or receive funding rate at the funding time (every hour). The sum of the paid/received funding rate should be even out in the long run, but it might cause a loss from the stakers in a short period of time frame.
Liquidation Clawback
Keepers might not be able to liquidate under-collateralized assets in time when price fluctuated a lot, and it might cause a loss from stakers.
These losses would be compensated by the spread charged from traders and Insurance Fund.
As a side note, the unbalance of AMM's inventory (long and short positions) would not affect the PnL of stakers because the AMM would always hold the 100% collateral of the unbalanced positions.
Basically, we fixed most of the Synthetix problems detailed here (front-running, skew of the debt pool, oracle, snapshotting attack):
Strike will use 3rd-party oracle solutions like ChainLink, Witnet, Tellor or others on the first release.