The way time travel works in the setting probably means it is poorly suited to their aims. Yes, it can in some alternate reality effect a change, but they want the current one to be course-corrected. So at most it'd create some offshoot reality, and to migrate all the souls to it would then take an additional abundance of aether in all probability. So I am not too surprised they never really bothered with it.
I'm more led to believe that it was an acceptable conclusion to him rather than him not wanting the WoL to side with him. It's subject to interpretation, and I do agree that the way he set up matters in Amaurot, plus his utter disappointment in his Garlean "son's" death (an interpretation supported by the poem in Ere our curtain falls) did suggest he was exhausted and wanted someone to pick up the torch, but none ever appeared.
His resolve and conviction to me seemed to be very genuine and supported by dialogue during the fight (where he asks who will be able to see their plan to fruition in his absence? - likely relating to his unique powers over the Underworld/Aetherial Sea being crucial to the task of awakening their dormant brethren in Zodiark), as well as various other materials in the game, like this. Moreover, it's clearer in the Japanese version that he had identified something special about the WoL's soul early on (some of the other versions misattribute this to the Oracle, IIRC.) So I believe that the soul rejoining and thus appearance of Azem for a moment (rather than the WoL's identity as Azem as such) took him by genuine surprise and led to him deciding to gamble it with a plan A and B (and however many more) already set in place. Had that act not taken him by surprise in that way, I could then perhaps agree that he had only one plan in mind, but in the end, it did, so either the WoL would prove themselves worthy to him to take on the burden of remembrance, or he would proceed with the plan and eventually restore the Source to its full glory.
I've little reason to believe that he did not genuinely wish for the completion of their plan, but for the exhaustion he endured in their toil. Even a victory now would still mean a long road ahead. Thus the contemplation of alternatives providing certain conditions were met. Hence Elidibus's decision to not draw on his memories seemed all the more sensible, to avoid distractions of this nature from forcing him away from completion of his task.
Yes, and we also know at this point that alignment to the energy/element of the primal is part and parcel of tempering. He seems to be mocking the idea that it equates to the subjugation frequently observed alongside tempering - something which various recent developments have now confirmed comes down to the nature of the primal and its intention to temper in that way in the first place. What he is referring to appears to be that immersion in the primal's element/energy. It does obviously orient them to spreading the primal's element, but at the same time it is distancing this from the usual beast tribe styled tempering where there is enthrallment over and above that.