Gotta make a choice on items like this. There are some good cleric usable mainhands that can be gotten at (or very near to) the same level of raiding required to do the harder tmaps/lifewards. Ocy's Tankard, Whip of Torment, Sanctified Mace of Reckoning (Cil is a little higher, but not too far off), the EDHK Mini orb, Firkaal 1hb are some examples of options.
I dont see how this is any different than having two secondary weapons to choose from. For example, Fjorelf (sp?) from GLib and Stormrazor from Sultan are both offhand only. It wouldnt make sense to make one or the other primary/secondary when there are plenty of mainhand options at the same level as said weapons.
Not to mention, you could just switch to Lifeward for rezzing and Orb for the mana =)