SLA will probably be the battery chemistry of choice for storage applications for years yet. In fact, I expect further advances in SLA technology to increase capacity and decrease weight for any given size. For example, last year limited production began in a couple of companies using Power Technology's * Reticulated Vitreous Carbon based electrodes. Unfortunately, these companies aren't mass producing this technology yet.

* http://www.pwtcbattery.com/technology/