There's not much to say to explain this suggestion, but I would love it if tomes were kept when TRing. We keep all our gear, we keep tomes if we lesser or greater reincarnate, why not keep tomes when true reincarnating? I am planning on TRing my current character. I just pulled a +4 tome. Obviously I'm not using it right away since I know I'm going to TR, but I would like to use it in her next life. However, once I do that it means I'll pretty much never think about TRing her again since I would lose that +4 tome and we all know that +4s are not easy to come by. However, if I knew I would not lose that tome when TRing again I would definitely consider it. I have a friend in a similar situation. I'm pretty sure that if we kept tomes when TRing more people would do it and if more people are TRing turbine will be making more money on points. I really can't think of any reason why this shouldn't be implemented, but if anyone has any thoughts on the matter, let's hear them!
Edit: This thread has received a lot more attention than I expected! Based on a lot of the discussion in the thread I would propose that this only apply to +3 and +4 tomes that are Character or Account bound. These are raid loot items and should not be lost. From a lore perspective since they are bound to your character you should retain the knowledge you gained from them. I think the easiest way to do this would be to simply have a tome placed in your reincarnation cache to use again at the proper level. I definitely do not think that people who have used +4 tomes in a previous life should suddenly have those stats at level 1 when they TR. If we were simply given a new +3 or +4 tome to use at the proper level when we reincarnated there would still be a market for the +2s to be used earlier on. I know, for instance, if I had a +4 int tome waiting in my reincarnation cache I would still use a +2 int tome at 7 in order to make use of the extra skill points early on.