Excuse the poor image quality, my phone is quite old.
In Game Grimoire could be implemented through an in game browser window. I've tested this myself. Destiny continued to run uninterrupted while I brought up Bungie.net and went to the Grimoire section of the website and it was totally functional.
If the UI was updated and a convenient link was placed so that people can reach their Grimoire, you'd placate a lot of the complaints and I don't see this being some incredibly difficult technical feat. I've already done it by hitting my playstation button, opening my browser and going to bungie.net. If you had an In Game UI option that made this a stream lined option for players, you'd find that they'd consider this the In Game Grimoire they were looking for. Not everything they wanted, but its a great start.
I don't mean to trivialize anyones job or make this to be quite simple, but this seems to be a far simpler solution than having the grimoire actually on the HDD. Maybe this feature wouldn't work on Last Generation consoles but it'd be a great feature for the PS4 & Xbox One.
So in Summary-
Add a UI Option so we can have a convenient access to Grimoire through a Browser bringing up the Grimoire page off Bungie.net.
- Maybe make it the mobile version of the web site so that the consoles can bring it up more quickly.
I welcome thoughts, ideas, and critiques.
[Just to readdress this, this is to address the problem players have with Grimoire Cards not being in game, while also being a much easier and technically feasible solution for Bungie]