I think keeping the validity long just removes incentives for people to bother fixing their setups. We've seen the shift from "Craig needs to spend a few days on certificate renewal every year" to full automation in most environments when the 90 day validity period was introduced, and shortening it to a week will only help further automation.
You'll always have the option to skip the hassle (for a small fee, unless a Let's Encrypt competitor joins the market), but I feel the benefits outweigh the downsides.
I personally would've preferred something like DANE working, but because the best we've got is DNSSEC and most of the internet doesn't even bother implementing that, I doubt we'll ever see that replace the current CA system.
Some software now uses short lived certificates and even with decent configurations, there is an elevated level of problems specifically because of certificates. Especially in networks that use a lot of segmentation with very restricted network traffic.
I think a short lifetime can be a security benefit, but it should not become a dogma. It should be employed where it really makes sense but as a general rule inconvenient describes it quite well.
FWIW you should run most ACME clients more often than that, just in case there's a performance issue or bug at Let's Encrypt's side. The tooling won't replace your certificates unless they're almost expiring anyway. Certbot's instructions will have you set up a cron job that runs twice a day.
> Some services do not load certificates while running and must be restarted
This is exactly the kind of software that needs fixing. Luckily for the critical, nine nines uptime cases where 5 seconds of downtime for the web server restarting is unacceptable, there are services that will sell you certificates valid for a full year or even longer.
I doubt year long certificates are going away soon. We're already years off Let's Encrypt ending their 90 days offering, for sure. The convenience factor isn't going away, at some point it'll just cost a bit more.