There are lots of folks selling cordless drill battery technology for powersports applications. Some go with the absolute minimum size for weight reduction in things like motocross bikes or other weight critical applications, and for those it probably makes sense even after factoring in the huge difference in price. However, when you scale everything up to handle a full zoot Harley dresser, you're only looking at a few pounds difference, and if you eat a really big breakfast before your ride you will lose any weight advantage gained with the Li battery. As for the lower self discharge rate, make sure you understand that only applies to the discharge rate when the battery is not connected to any sort of load. If you leave it connected while your bike sits for weeks or months, then it definitely will discharge as the always on items on the bike continue to draw current. The Li has a lower self discharge rate than a standard lead acid battery, but the latest AGM's don't have a high self discharge rate either. Maybe it would be a good selling point if you planned to buy one and let it sit in the basement for a couple years, but otherwise it's just more marketing smoke that has little impact for the majority of customers. In other words, don't throw away your battery tender if you plan to let your bike sit for any length of time unless you plan to disconnect the battery.
Lithium is a highly reactive and hazardous material, regardless of what the advertising copy implies, and lot's of Li batteries have had safety issues, including laptop batteries that caught fire and similar problems with certain electric and/or hybrid car batteries. So read those ads with a healthy dose of skepticism.
The time will come when the older lead acid technology will probably be pushed aside by Li-ion and other technologies, but only when the economics make sense. Right now Li-ion is way too expensive to become the mainstream starting battery for vehicles. If you race small motorcycles with kick starters, the high cost but lower weight might be justified. If you ride a 900+ pound street bike loaded with electrical accessories, IMHO it's just one more of the many things being offered for sale that isn't worth the price. If you want to pay three times as much just for bragging rights, go ahead if that's the sort of thing that impresses you and your friends. I'll stick with my AGM for now.
Jerry