Ores and smithing related items will fluctuate according to future updates, if any.
Seeds and traditional farming resources are obviously deflating rapidly across the board.
Baring any new school skilling updates in 2019, the other skilling resources like raw fish, planks, etc will become stagnate.
Combat equipment will go up and down the chart depending on the new bosses and ED(s). But mainly, I think they stay within a trading range.
Big ticket items, especially the ones in the vein of phats etc will remain "artificially inflated" as the Jmods called them.
In a nutshell, if you are a for fun/entertainment player, you will more than likely be seeing a stable economy in RS3 in which you can get most of the stuff yourself with your own time. This is also good to ironmen too.
Inflation is pretty much always active; just how much changes over time.
Negative inflation or deflation, which is exactly what's happening now in RS3.
Jmods confirmed that.
When did Jagex confirm this?
GE Tax? We think about it a lot. 'I think the only way we can only tax stuff on GE when we can trade everything on the GE. So when we can trade over max cash on GE, that's when we'll probably add something.' You don't want to tax Yew shieldbows and other low level items, because it'll discourage players to sell but there does need to be a tax on trading big ticket items. We were in a period of deflation last year which is the complete opposite of what people think. Inflation on big ticket items like partyhats is completely artificial and not due to inflation in RS. Deep Sea Fishing sunk out a lot of money as well. Invention removed a lot of items that would have been alched. High alchemy is the largest source of money in the game. With the Smithing rework, we're hitting this more with giving more incentive to turn items into XP instead of alching them.
They are also absolutely correct that as M&S rework being released now, smithing has become a source for xp instead of gp. The stone spirit debacle and mob loot table nerf also helps to curb gp source.