Agreed.

My programming intuition sounds the alarm when I see solutions with a number of unknown downstream consequences. I don't like code with unknown risks.

At a minimum, features can be tested for several years on for example Liquid Network and be evaluated there.

Among the claims of lower L1 fees, I don't trust such claims for several reasons. Tx fees can already range from $1.5 to the tx's upwards of $200 that were seen for a week right after the halving. This tells me that the tx fee pricing is largely dependent on the willingness of participants to pay a certain amount. If there is a willingness to pay high fees, then we can improve the bandwidth all we want on L1 without achieving low fees.

As far as the solutions involving increased efficiency for exchange transfers, I doubt that they would make much of an impact, if exchanges want to use them.

For the other proposals I am also unconvinced that there will be actual increases in L1 efficiency. They may or may not be significantly helpful.

My main concern is the ability to whitelist future addresses, i.e. blacklisting all addresses outside of the whitelist. It is not inconceivable that governments at some future point, in an attempt to hinder the competition against CBDC's, may decide to require exchanges via regulations to apply whitelisting schemes, to lock bitcoin within an approved framework of future addresses. Even if such regulations are introduced and then abolished at a later date, the whitelisting protocol would already be in place. If central planners can abuse a mechanic on L1, I would rather see such a mechanic on L2-L3. 

 Expanding further, the idea that 8 billion people can use L1 always struck me as strange.

I don't have data on the average number of transactions per block but it would seem to be around 3500-4500 tx.

If we could achieve 7000 tx per block on average then that would translate to a million tx per day (144 × 7000). Dividing 8 bn people with 365 million tx per year gives a bandwidth of ~22 years for an ideal scenario.

A more likely figure for the current bandwidth is 4000 tx per block, yielding 576k transactions per day, giving 210 million tx per year. This results is ~38 years for the world population bandwidth.

Even if the demand pressure on L1 is far lower than 8 billion people, some percentage are children without the need to move savings, some may not be using Bitcoin at all, some may be using mainly L2-L3's, we are still at a situation of some participants outbidding others in order to have their tx included on the main chain.

The idea that "everyone must be able to use L1" is naive in a scenario where almost 8 bn people are using Bitcoin. Not all participants will have the funds to compete for blockspace, even if we had 7k tx per block or more.