OK I'm not an expert on the new GTLDs, but I recently spent a morning looking into them out of interest. My understanding is that the idea of pre-reserving is a misnomer. These GTLDs are going through phases of registration, including a period where trademark holders can request names for their trademark in advance of the general registration phase. These are the only people who can legitimately "reserve" a name in advance. The general public, on the other hand, will be able to buy names all at the same time at general release.
I have seen some providers offering "pre-registration", but what this really is is registering your interest only with that provider before the other provider's customers. But even if you "pre-register" with that provider, that provider will not try and place your order with the domain registrar until the GTLD goes live, and at that stage there will be other providers also trying to register GTLD names with the registrar, and they may have customers who want the same name as you!
My understanding is it will be a free for all as soon as a particular GTLD is released.