I am against this guild hopping. This may be restricted to an extend to avoid exploiting the current situation. In my opinion, Once you left your current Guild and joined another Guild, there might be some restrictions (cooling period) to join back to the old guild or to any other guild. However, I don't support that the cooling period start immediately he left the guild. It may apply only if he joined another guild and wished to hop that guild also before the cooling time.
Because, at present, if a top 50 player wishes, he can hop "n" number of guilds in a day for getting enough trades (many guilds are using different trade rates which can be exploited), mot/pol (he can get additional chances of blue print and also to get his buildings polished/motivated to max.), extra battling chance (The neighborhood members may be scattered in many guilds and hopping gives the player a chance to fight with all of them, though we can't do anything about this because a player has chance to fight all his members if he leaves his current guild and stay guild-less but at this time he will not get the liberty to exploit any other guild for his advantage of mot/pol or trading).