Is scaling Bitcoin heading it to a dead end? The immutability of any given blockchain is reinforced by the total hashing power behind it. Proof of work (ergo a financial commitment) is a necessity to ensure the party verifying transactions is incentivized to do so honestly.

Currently (April 2018) mining profitability is relatively low and may soon become limited to those with really cheap electricity. This is before any scaling solutions have really come into full force with Bitcoin. 

With the next block halving in 2020 (one of many more to come) and scaling solutions becoming mainstream will there still be enough incentive for miners to support the blockchain?
You're confusing different things here.

Parties incentivized to verify transactions are those that receive payments. Miners are only incentivized to do Proof of Work. (Although they have to be careful to not include invalid transactions while doing so.)

Mining is actually very profitable now. You can tell by looking at how fast the hashrate keeps growing. In the long term though, profitability is supposed to be near 0 because of competition: if there's free money to be collected, it would be weird if nobody came around to take it. Those who have cheap electricity inherently have an advantage.

Scaling solutions don't have much to do with any of this, other than possibly hurting the entire system by having blocks become too big. Scaling implies more transactions per block so which means, all things equal, more total fees for miners. Of course not all things are equal in practice, but assuming enough demand to fill blocks, a new equilibrium will be achieved.