This is what I hope to see in Wave 9.
Wave 9 should be announced shortly after the release of wave 8 and release towards the end of summer. There may be a few other announcements between the announcement and release of wave 9, Imperial Veterans has been announced already, and a rebel and scum equivient, and the first scum ship is being speculated. The next Star Wars movie is Rogue One next Dec - so we may see a small wave coinciding with the launch of that movie (it is unlikely there will be another core set) but that will be much after wave 9.
Over the next few months we can expect to see more short stories fleshing out the various scenery characters in TFA. The New Republic Bloodlines novel will be released in Mar and is a prequel to TFA by 6 years. Marvel comics has more OT era stories finishing and coming up including features on C-3PO and Chewbacca, along with the regular titles, Star Wars and Darth Vader. OT era short stories are extremely likely as well, and it is possible that Disney allows games like Battlefront to feature more OT and between OT and TFA story content.
FFG has their own Legends (non canon) products going - and as X-Wing is also a legends game - we could see some cross overs.
I'm expecting the next wave to have 4 ships as per wave 8, with 1 rebel, 1 imperial and 2 scum. Scum is still playing catch up and has much less ship than 2 original factions.
Rebels: Expecting a small ship of some sort - the N-1 is an option with Leia and Shara Bey (as recently featured in the Leia Marvel comic); the Thallanx from FFG's AoR RPG is another - its a stealth fighter with similar cababilities to a Z-95, even a legends New Republic era X-wing such as the T-65XJ might not be out of the question.
Imperial: Expecting the Upsilon-class shuttle or TIE/sf to show up in the next 2 waves and completely release all the starfighters from TFA. Either works, but the TIE/sf would be a more significant ship as compared to the Upsilon due to it being the first imperial turret upgradable craft.
Scum: Expecting a large and small or even 2 large - large ships seem to be the theme of scum - with their limited number of ships they already have more large ships than either rebels or the empire. For small ships, the Dunelizard and Drexl are the most appealing as they both can equip astromechs - an upgrade only used by the Y-Wing and the upcoming JumpMaster 5000. For large ships, the Scurrg H-6 seems very likely, having been released in Armada (Strangely as a Rebel ship); other likely ones are the Banshee/Shadow Caster and the Gauntlet fighter. If a second large ship is released, I hope to see a large but not heavily armoured craft - something like the Preybird or the Ixiyen. Scum is already heavy on big expensive large ships and could use lighter, and less point heavy large ships.