I have found WHMCS to be really handy even though I am just scratching the surface of its abilities.
One thing that I already think would be wonderful to have is the ability to run multiple/independent client areas on multiple/independent sites.
Why would this be useful? Sometimes one may want to run different independent web sites for different brands/products of the same company. Many IT consulting companies do this. And have different client areas for each site. I will admit I am looking at this more from the additional products or brands a tech company may want to manage (as opposed to only web hosting).
CMS software also already do this. You can have just one install in the root of a domain or httpddocs and yet run multiple web sites by either using db prefixes in conjunction with a separate settings.php or config.php for that site or even by using a totally separate database.
I think it would be a killer feature for WHMCS and could be priced differently from the regular version.
Does anyone else also think this will be good to have in the future?