You don't get it do you? With a Rising Rivals-On format that cuts Platinum Base Set and the SP Cyrus Engine (Cyrus's Conspiracy, Power Spray, Poke Turn, & Energy Gain) from the format while leaving us with sets that haven't yet been fully been in the format for 2 years minus the Diamond/Pearl sets due to Majestic Dawn-On for which reasons are unclear according to Pokemon USA and TPCi.
Like I've said before and I'll say it again, there has never been a set in the Pokemon TCG that has been legal for just 1 Modified Season alone, every single one was legal for at least 2 seasons before rotating out of the format so yes Rising Rivals, Supreme Victors, and Arceus will stay in the format regardless that the HGSS reprints in Call of Legends is garnering hype for a HGSS-On format which would leave to just a metagame with LostGar and Counters for it.
A metagame like that would be very bad, cause players to quit the TCG, and stagnate things further. The reason for the HGSS Reprints in Call of Legends is for the upcoming Unleashed-On format after Rising Rivals-On format that crm103top08 already mentioned earlier in this thread. It makes better sense than a HGSS-On format. No Charizard? phmph... No Bebe's Search and Palmer's? No Absol G Lv. X tech against LostGar? See where I'm getting at? We'd also lose Expert Belt as well.