Hey, EA_Cath
In particular, buying zen garden plants, including which you don't have, like in mobile version, is top 1 addition needed, so enlightened achievement wouldn't be that unreasonably hard to get.
Then I figured some great ideas of adding new content:
1st and most obvious, minigames. There are couple of unique minigames which are in some console versions only, getting them to the definitive version of pvz would be great. Or nobody wouldn't mind if new minigames were figured out, as long as they are fun.
2nd are environment features, which include: Zombie count from mobile game of pvz and leaderboards with your friends on steam; House customisation from console version, which you can also compare with your friends on steam (would be cool if friends could also see zen garden of each other); Cant forget R.I.P. mode original soundtrack.
3rd I will mention skins. Really liked them on Christmas, sad it didn't happen again. Totally wouldn't mind if skins weren't temporary, so you could equip or unequip them for plants or zombies. Would be cool if there were permannent skins (1 for each plant, could bought in the shop, 20k for a random skin e.g. or one for an achievement) and temporary on holidays etc, which you get only by playing during period of time.
4th I would probably suggest R.I.P. mode gameplay expansion or improvement (I made a doc - suggestion of modifiers idea earlier for example).
5th and final one would be pretty straightforward, what if chinese bonus level would be a sequence of levels? Instead of 1 random level, there were 3-4 levels with unique layouts (unique water or roof lanes location, or the layout with first 3 lanes being roof tiles and other being water). Adding new zombies from pvz chinese version to that level(s) is also a good idea I guess.
P.S. Im not asking for everything to be implemented but I expressed some ideas, from which 1 of the 5 things could be taken along with bug fix and zen garden plants buying feature in order to make a giga W update, in my humble little opinion.
(Edited) Some balance changes are also needed to VS mode in coop