Anything posted here is pure speculation.
I don’t believe there has ever been an established product cycle for Absolute. Releases seem to come when there is a worthwhile upgrade to sell based on the availability of new or upgraded constituent products, rather than being calendar driven.
HALion has gone a while without a paid upgrade. I would not be surprised if the key new feature of a new Absolute version was HALion 7, perhaps with one or more new synthesis engines (FM?) and at least one instrument using the new engine. If there is a new HALion, I would expect a version bump in HALion Sonic to HALion Sonic 4 with the inclusion of any new instruments from HALion 7 but no other changes.
Most of the new HALion add-ons that have been released in the past year are sold by Steinberg on behalf of a third-party developer (Cinematique Instruments, Sample Fuel, Msixty7 or e-instruments). I doubt any of these add-ons will be included in Absolute, but I may be wrong. I believe Electric Bass is a Steinberg add-on - if so, that might well appear in a future Absolute.
I’m doubtful there will be a new version of Groove Agent in the near future - Groove Agent 5 was an improvement over Groove Agent 4 and was the key new feature of Absolute 4.
Steinberg might include one or more of the existing Groove Agent add-ons in Absolute 5 - if so, I would expect the chosen add-on(s) to come from amongst those with lower retail prices. I would expect the premium add-ons such as Simon Phillips Studio Drums, Simon Phillips Jazz Drums, The Songwriter’s, Nashville, Metro Heights and Bouncy Vibrations to stay as separate purchases only and not be included in Absolute.
I doubt The Grand will see any further development - it works as is. There is likely little scope for return on investment on any enhancements considering the marketplace for piano VSTs is saturated.
Absolute 4 got the new Padshop 2 and Olympus Choir Micro library mid cycle (if you own Absolute 4, have any interest in either of these and haven’t downloaded them already, all you have to do is upgrade to the latest eLicenser Control Center, run Maintenance, download and install). There is very unlikely to be a Padshop 3 in the near future! It is possible a future version of Absolute will upgrade Olympus Choir to the larger Olympus Choir Elements product, though this may well stay outside Absolute.
If Retrologue is further enhanced then I would expect the upgraded Retrologue to be in a future Absolute. However, as an upgraded version of Retrologue is likely to be included with future versions of Cubase and Nuendo, an upgrade to Retrologue would be a limited incentive to buy or upgrade Absolute if you also own a Steinberg DAW.
I doubt any of the existing Iconica content will be included in Absolute. Currently even the cheapest Iconica product is fairly expensive and the only bundle that includes any Iconica content is Iconica Opus (which is Iconica Sections and Players bundled with Iconica Ensembles). As someone who owns Iconica Opus, I can’t think what you can strip out that leaves a viable orchestral library other than removing microphone positions and perhaps some of the round robin samples. These changes would somewhat reduce the realism and sound sculpting possibilities, but not significantly impair the core functionality. Such a stripped down product could devastate sales of the full Iconica products if it was significantly cheaper than the current products or bundled with Absolute. I think the existing Iconica products will stay as they are and stay outside Absolute. Absolute already has basic orchestral functionality courtesy of HALion Symphonic Orchestra.
One possibility for future enhancement of Iconica is solo strings - the current version of Iconica Sections and Players only contains string sections. Solo strings would allow for solo string players accompanied by one or more other players, also string chamber ensembles. It is possible a solo strings enhancement would be sold as part of a new version of Iconica Sections and Players, or as a separate Iconica Solo Strings product. If there is an Iconica Solo Strings product in the future, this could conceivably find its way into Absolute though I somehow doubt it will.
In summary, my guess for Absolute 5 is new versions of HALion and HALion Sonic, also the inclusion of Electric Bass and perhaps one or more of the existing Groove Agent add-ons. Less likely, but possible, is the inclusion of Olympus Choir Elements and/or a new solo strings HALion library.