No, there is nothing missing from the series. Nostalgia has no place in the current show.
Eh thats pretty debatable. Personally i think anime lacks humor and adventurous aspect, dynamic it used to have before. I could receive such vibe from OS and on good part in AG, but from DP and even BW? Not that much. There is almost no continuity nowadays and cohesive story is pretty weak point nowadays as well.
But i guess it depends on personal interpretation what may be your cup of tea fulfilling interest.
Obviously they don't. Given he stayed in the anime for 8 more years after Johto ended and they didn't do much of anything with him.
To be fair he had pretty good role in Kanto and Hoenn receiving perfectly fine amount of focus for supporting character. Got shafted abit in Johto but still had memorable moments, and was screwed over in DP(although i don't think he was bad by any means, it just happens he was sidelined too much).
That aside when talking about prospect of older character coming back again such as Brock, we shouldn't focus on past and what has been done but on future and possible new, exciting stuff writers can come up with him. As years pass writers improve, learn from past mistakes and try to add new stuff to maintain people interest.
When writers introduce new ones or reintroduce older characters after long absence they have to make him memorable just as much as new one. Since return of long time absent character would serve as something to shake up anime bringing twist and unpredictability, its guaranteed that writers are going to put more effort in character itself and its story to have audience accept him easily as part of cast again.
Their aim is in capturing viewers interest for characters they introduce, and i believe any previous character including Brock could become memorable and appealing to wide group of people again if he is given some significance, new purpose through which his story could be continued.
. He's got the potential, now do they have the talent?