Berries: Obviously will be the same berries with the new, GenIII names.
Gold/Silver Leaf, Brick Piece: Were junk you just sold for cash anyways. And they were only held by RGBY Pokémon traded in. These can safely be left out.
Slowpoketail, RageCandyBar: These are integral to the plot and MUST be included by some means.
Apricorns and Kurt's Pokéballs could be handled in one of three ways:
1. Kurt just sells you the Devon balls for cash.
2. You can collect Apricorns and Kurt will turn them into Devon balls.
3. My preference: You can collect Apricorns and Kurt will turn them into the *correct* Balls. D/P/P are programmed to display out-of-range Pokéball IDs as plain old Pokéballs which should work well enough. The Pokéball field has enough room to allow for 256 unique kinds of Pokéballs.
As for the supposed parallels between the old and new Balls, they work only loosely, and some are just similar in name alone. Let's compare:
Fast Ball: Effectiveness enhanced against species which tend to flee. (In G/S/C, this didn't apply to the Catdogs. If the Fast Ball makes an appearance, I hope this changes.)
Quick Ball: Effectiveness starts out high and decreases as time passes in the battle.
Nothing in common besides name.
Level Ball: The ratio between your Pokémon and the wild Pokémon determines the effectiveness.
Nest Ball: The wild Pokémon's level alone determines the effectiveness.
Similar, but the Nest Ball becomes as useful as a Pokéball against high-level foes, whereas the Level Ball retains some usefulness if you have high-level Pokémon around.
Lure Ball: Effectiveness enhanced against Pokémon hooked by a Rod.
Net Ball: Effectiveness enhanced against Water and Bug-types.
It would seem that the Net Ball is better, but this wouldn't exactly be true if the Lure Ball's effectiveness rate is made higher than the Net's.
Heavy Ball: Effectiveness increases depending on the target's weight. Perfect for those XXL Legendary fatsos.
Has no real counterpart in the GenIII/IV Balls.
Moon Ball: Effectiveness enhanced against Pokémon from evolutionary lines involving use of the Moon Stone. (Nidos, Jigglypuff, Clefairy, Skitty)
Dusk Ball: Effectiveness enhanced in caves or at night.
Nothing in common. The Moon Ball seems quite niche, but it has such style!
Friend Ball: Pokémon caught in one start with a happiness value of 200. (In G/S/C, this was reset upon trading. This could be changed, at least for a receiving HG/SS game.)
Luxury Ball: Pokémon caught in one gain happiness more quickly.
I'd have loved to be able to catch a Buneary in a Friend Ball.
Love Ball: Effectiveness enhanced if the target Pokémon is of the opposite sex from the Pokémon you've sent out.
Heal Ball: Pokémon caught in one are healed to full health.
Nothing in common but the colour pink.
These Pokéballs would definitely add value. Especially if you care about the style of your Pokéball's opening effects.
I wouldn't cross off the possibility of a "firmware update" over Wi-fi just yet. It's not their style, but it's certainly on the table. Otherwise, the usual concessions of held items flying off and Pokéballs showing up as plain will occur. I hope these shortcomings don't deter GF from adding back these items.
