If it's like Killing Floor 1 (and working with what we know about KF2's updates), the updates will work like this (keep in mind I'm talking content updates, not balancing patches/fixes or anything):
01.) There will be free content updates for the game for a few years after launch. All new maps will be free, a variety of new weapons will be free and added to the class weapons (each class should slowly get several new weapons over time), and it's been confirmed there also will be enemy updates to add new enemies/bosses into the game.
The Baton/shield is under this classification of updates, since the game is just out they're now going to be adding new stuff to the base game free of charge for all users, and there will be more weapons added for all classes over time. This said, not all weapons will be free down the line, which leads us to the second thing...
02.) DLC. Now, the DLC may not work exactly like Killing Floor 1 as there now is the crate/drop system in KF2, but in Killing Floor 1 cosmetic costumes & community weapon packs were paid DLC. As there's a drop system now which basically gives you the same thing the old KF1 DLC did, I'm not sure if that will replace or these are coming back. But to explain in basic, costumes & community weapons (weapons made by the community and licensed for use in the game) were paid DLC in KF1, they seem to be the dropping system now in KF2.
03.) Crossover Promotions. This was in KF1, and is in KF2 on PC for the moment. Basically, owning other games will get you some exclusive costume/characters/weapons in KF2. The ones in KF2 (PC-only right now) are:
-Horzine Elite (outfit) & all Horzine Elite 9mm variants (cosmetic weapon) for buying the buying the game in Early Access.
-Tom Banner (character) for getting the Deluxe Edition or for owning Chivalry
-Anton Strasser (character) for owning Red Orchestra 2
-Zweihander (Weapon) for owning Chivalry.
-DJ Scully (Character) for owning Deluxe Edition.
-Mr. Foster PC Gamer DOSH (cosmetic) from PCGamer promo.
-Alienware helmet (cosmetic) from Alienware promo.
04.) And the favorite of most, Holiday Updates. These are free as well, obviously. To explain this, these are free updates that usually include one new permanent map for KF (that's loosely based off the holiday theme), all of the enemies get new skins/some get new sounds that are thematic for the holiday (in KF1 as an example for the Christmas event, Clots get dressed like elves, the Gorefests become gingerbread men, the Crawlers became dressed up like reindeer, Fleshpound became a Nutcracker, etc.) that all enemies on all maps will be while the holiday event is going on (usually 2-3 weeks), and often something new was also added to the game (in KF1 and assuming KF2 as well), IE new weapons, new costumes, etc. Usually it'd be 1-3 new weapons for the classes and one new costume. Also new achievements get added, and there'd be a holiday challenge if you can do a certain percentage of the new holiday achievements before the holiday event was over you'd get some timed exclusive reward costume (like a Santa outfit for Christmas, Grim Reaper costume for Halloween, that sort of thing, which would only be available for a limited time during that event).
Also new music usually got added to KF1 for the season, which would play during the event on maps (and play after the event on the new released holiday map).
The holidays that Killing Floor 1 celebrated:
-Twisted Christmas
-Halloween Event
-Sideshow Summer
-April Fools
Christmas was celebrated every year under 'Twisted Christmas' and was consistent. Halloween was celebrated every year from 2011 onwards, though the theme of the Halloween event would differ (it first was "Sideshow Amusement Park" themed, but later that sloy got taken by Summer so they made Halloween Hillbilly themed), Summer & April Fool's are on and off holiday things not celebrated every year and kind of alternated with each other which would be celebrated. Summer would usually be Sideshow themed, and April Fool's was a grab bag (one year was Portal themed for a crossover around Portal 2's release which added a new Portal-themed map to Killing Floor).
So those generally are the content updates, just new content updates (these will be more frequent for the year or two after release as they add more content to the game more actively), then the 4th updates will take over more afterward if it's like KF1 (where there's three big updates for the game a year around Summer, Halloween, & Christmas time).
