-snip-
It's even cheaper than that. I can find an 8 TB hard drive on Amazon right now for under $130. Even overestimating growth at 150 GB a year (so every block around 2.8 MB), that's 53 years to fill 8 TB at a cost of around $2 per year.
The limiting factor for running a node going forwards has never been the size of the blockchain, but rather things like the size of the UTXO set and the speed of verification.
- Optimizations: Are there any ongoing efforts or developments within the Bitcoin protocol to optimize resource usage and improve scalability?
There are proposals for how to limit the growing size of the UTXO set, such as utreexo. If you want to limit the growing size of the blockchain itself, then you simply run a pruned node.
Offchain solutions like Lightening Network has been very effective in taking load of the main chain and allowing users make smaller transactions at a much cheaper rate, securely.
Have they? Lightning's total capacity isn't even 5,000 BTC, and each channel open and close requires a not insignificant on-chain footprint.