It originally existed in Beta, but popular consensus was to remove it. You're welcome to edit the template and add it however.

GJ 2.5 will feature a new template system (shortly after 2.4 release) that will be removing a lot of parameters and making a lot of changes users want to require template changes, this is due to the over bloating of configuration; it needs to be simplified. The new template system will also make it extremely easy for those unfamiliar with PHP and will only require minor HTML knowledge to edit. At this time I can't say specifically what parameters will be removed or simplified and will provide more details with 2.5 release.

2.4 is primarily a bug fix release and introduction of a new data layer API to reduce query count by 80% and reduce memory usage by 20%.

GJ 2.4 will be available when it's done, sorry I don't provide release dates. My goal was end of last week, but was tasked with developing a new payment gateway for CBSubs. I am hoping to have done by end of this coming weekend, but that is also seaming less likely as more issues are found and requests are made.

What exactly is your problem with invites? I can not confirm your issue, they seam to be sending fine. Are CB emails working at all? Have you tried mass mailer within CB User Management to ensure emails function? Have you tested with debug mode enabled and maximum error reporting configured within Joomla global configuration.

The templates have already been minimized. The feature ticket to redo them has been rejected. I've no plans to redo the system any further at this point. As it stands now it uses minimal coding, but full capabilities of PHP classes and functions even specific to a single template file.