How can we improve WHMCS?

It doesn't matter how big the database is, caching helps reduce the load on the server. This may not seem necessary when you have a bunch of users logged in, and may not matter much when you have server resources to handle more users. But, when you start getting into 1000s of users concurrently using WHMCS and every single page load querying database, you'll start seeing performance issues.
WHMCS is not really dynamic, not many things in WHMCS are updated in real-time or need to be updated every page load. Plus, cache can be invalidated on user action (ex: submitting a form or clicking a button) so data is refreshed. Plus, it should be expired. For example, if your bandwidth graph/data is updated every hour or so, why would you query data from database every page load? That doesn't make sense.
Certain things can be excluded from cache, like shopping cart.
The point is, WHMCS should provide support for object caching so we can use it if needed. WHMCS has an article about high availability that's based on a talk from CEO (i think). Caching and high availability go hand in hand.

I've been all game for caching until I stepped back and remembered this as well. Like @Johann mentioned, I'm not sure how caching would make sense in WHMCS, because everything is dynamic. It sounds nice, but isn't practical. We also have a 1GB database, and on AWS, everything loads extremely fast. If anything, a focus on database query caching would be nice, but not much needed, as as long as the server/database have the resources, the load is already very fast.

Our database is 1GB (because of tickets content), and web pages loads within 0.7 sec, i don't see how caching would help in anything in such dynamic CMS

There maybe some issues with Memcached if not secured properly given volumetric attacks increased substantially.

https://www.wired.com/story/github-ddos-memcached/

But generally speaking, I do vote for the implementation of caching. I would prefer a module approach the enables external service providers such as StackPath.

Any possibility of this happening in WHMCS 7?

+1 from us. Performance is also a big factor for customer satisfaction and a deciding factor for a purchase.

+1+1

I have a lot of dedicated servers, the product page takes about 4 seconds to load.

I now use an HTML page to combat this and link the server product directly to its configurations page.

It's kinda lame I had to do it this way.

There should be Memcached caching for WHMCS .

caching is a must for any application it should be prority.

I'd suggest Redis for larger deployment or APCU for smaller

Redis is enough

Same!! This is a must!

I like this idea.

Redis or varnish would be a good option for speed improvements.

I also vote for this idea, hope it would become a reality soon.