3 months is very short . Do LE have any future plan to increase expiration time ?
I think the short answer is no.
As far as I’m aware there are no specific plans to change it, on the other hand it may increase, or reduce in the future. Since it is an automated renewal system, then once set up it shouldn’t really matter if it’s one month, or 1 week.
so its better to buy a certificate with longer validity and sit back.
why it is so hard to increase expiry time ?
i have web server and LE client running on different server everytime i need to run LE client then transfer key,certificate files to another server. also need to point domain to LE client server ip for domain validation 
why do you need to manually transfer certificates etc ?
I also have websites where the LE client isn’t on the same server ( in cases where the server has unusual OS and I don’t want to install the main LE client) - I use https://github.com/srvrco/getssl to automate things. So although I have multiple websites, on multiple servers, it still all happens automatically with no manual intervention ( after testing anyway 
)
You can read this topic https://community.letsencrypt.org/t/pros-and-cons-of-90-day-certificate-lifetimes which discusses about the certificates lifetimes.
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