Theoretically there is still chance for Brock to make cameo appearance since new generation at least wont begin until end of 2013. Not to mention his flashbacks in Dawn cameo could serve as foreplay announcing his return in person eventually.
I would like to see some update on his character, pokemon and how is doctor career progressing and i believe his similarities with Cilan create foundations for some worthy, interesting interactions. Meeting between two older make sidekicks who are like older brother to group and cook contest to determine who is better chef could besar some fruits on table imo.
It would be interesting to see him doing field work and research on pokemon outside of center along with learning about new ways of curing from first hand by meeting other specialists not only relying on books making sense serving as way to enrich his knowledge which could help him when passing test and examiners in future trying to become doctor.
And seeing him battle for old time sake would be appreciated too. With such impressive pokemon arsenal like Steelix, Croagunk, Foretress, Marshtamp, Crobat, Sudowoodo its real shame we never saw him battle much.
The better question is: Do people even care enough about Brock to warrant him a cameo?
If you ask me such way of thinking only further encourage having anime imbued with lower quality which suffers from intermittent connections with past, very little continuity and lack of cohesive and stable storyline. Which is anything but good with constant cast cycling not contributing much in long term to ensure appeal and loyalty among fandom to broad show popularity.
Even if we get sick of certain character that doesn't mean he couldn't restore in future appeal he used to have making us appreciate him again. Or create different spin to him/her adding new interesting dimension to it.
Instead of stopping to care altogether turning blind eye to problem, avoiding to directly face with it.
Personally yes i miss Brock, and many other people out there miss him too having fond memories of character wanting to see him again. Granted there are other characters which i would rather have return who haven't been seen for years like Misty, but i still appreciate Brock contribution to anime and all positive things he did deserving some recognition. No one deserves to end up abandoned and erased from face of existence.
Admittedly demand for Brock isn't so prevalent around here but judging by youtube, deviantart, pokecommuntity or tumblr Brock still has respectively big following with number being counted in thousands. Not even counting those who either don't come on internet or don't post on pokesites .
When it comes to Brock, I see a lot of people talk about how stale and annoying he ended up becoming. I see little fanart and fanfiction for him. People rarely state he's a favorite of theirs.
Fanart and fanfiction isn't credible indication through which we can base someone popularity though, because not every character which is popular has lot of appeal for shipping or invention of fanon stories about himself.
Needless to say just because you see sizable portion claiming Brock got "stale" doesn't mean something is true.
For instance "many like junk food, but that doesn't make it fine cuisine".
It's weird because aside from a couple of COTDs, I really don't care much for the other main characters like Misty and Brock, probably because they degenerated so much.
I presume your speaking for yourself, because i didn't found Misty character stale at all with most of her highlights coming from Orange Islands and Johto. On contrary just when writers finally started to do more with her story exploring on water master dream with Whirl Cup making things become interesting which was fresh breath of air after usual supporting role character was put in, she got replaced.
Being followed with some notable growth in chronicles and AG cameos earning sisters respect, taming Gsarados, releasing Togetic etc.
Value of character shouldn't be determined by how much focus he gets, but by how much he contributes to anime appeal and Misty definitely managed to add tension and vibrant dynamic in cast, helped Ash grow as trainer, often contributed to resolution of plots in episodes and got some intriguing growth herself too.
Granted writers made slip with her in mid Johto being often on sidelines, but way i see it with Master Quest and onwards character was successfully brought back on right track managing to keep appeal.
Same applies to Brock until DP where he got shafted too much for my taste i thought he was handled pretty good especially in AG saga. I enjoyed in his interactions with AG cast still having his moments, addition of Max helped his character by having someone to who he could relate to and his breeding career got some notable focus too often helping to resolve alarming situations regarding wild or endured pokemon, took care of suck characters like nurse Joy etc.
Likewise he was more active than i can say for Johto too having some notable moments like battling May in contest, battling TR with Ash in tag match to save Pewter gym, learn about new ways to prepare food and keep pokemon in top shape(like pokeblocks etc).
I just don't care much for them and neither do a lot of fans.
Any proof to back this up? Because i can assure you how internet is full of people who like Misty character with demands for return for cameo or even return to cast still being respectively big. Even after such long time being equally popular to other girls (arguably even more).
I'm surprised by the number of people thinking/wanting Brock will/to return (as in travel) for Gen 6. He's a doctor now and he'll have to study hard for that. That was the reason why he switched most likely, so they could take him off the show. /that was a bit of a rant but now on topic/