The changes to Tank Conversion are regressive.
It looked, in the previous beta, like we were getting seperate Conversion Cost and Production Costs, which reflected the amount of time it would take to change different components on the tank, similar to how Ships get upgraded. The tooltip was there, it just hadn't been hooked up yet.
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Now Conversion Cost has been deleted altogether. You have to pay the full Production Cost to add even a small upgrade to your tank. The game thinks you're building a whole new tank!
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Above is the Panzer II Ausf. a that Germany starts the game with. Pretty basic tank, lets add some smoke launchers.
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The smoke launcher is the 3 canisters on each side, seen here on a Panzer II Luchs (image from Wikipedia).
Below, we are converting our Ausf. a tanks to the Ausf. b model with the smoke launchers. Shouldn't take long, to bolt on the new module, right?
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Wrong. The game charges us for an entire extra tank. We must rebuild the entire thing, from the ground up. This makes tank conversion worthless. I would say it is broken.
Effect of Conversion Techs
There are 2 x Conversion techs we can research which each give a 40% bonus to production output, when converting tanks. Each of these techs takes months of research, and doesn't really alter the production rate of this tank all that much:
5.63/week - with no conversion tech
7.07/week - Improved Equipment Conversion (1937)
8.82/week - Advanced Equipment Conversion (1939)
Given we are only bolting smoke launchers onto the side of the tank, I would say that the techs are not the solution.
Different Types of Upgrades
Finally, without the Conversion Cost mechanic from the previous beta, there is no difference to the type of upgrade you're doing to your tank. We only added smoke launchers, but for a similar conversion cost we could change to a 3-man turret, we could fit a high-velocity gun, we could fit radios, we could even apply thicker armor and a bigger engine, we could do anything we want, because we are being charged the cost of a full tank anyway.
In WW2, tanks often received small upgrades, as new technology was developed, or to overcome deficiencies they encountered in a given theatre against a certain enemy. Unfortunately, we are presently unable to do a small upgrade, such as adding a newly-researched radio, or bolting on armor skirts, as we get punished for doing so.
The best example of this system is Ship Upgrades in MTG. As in real life, replacing the main armament of a ship is balanced so it's unattractive, but equipment such as ASDIC, AA guns, Depth Charges can be added to the platform to fit the tactical or strategic situation. It's good gameplay, with real tradeoffs.
I would propose that Conversion Cost is brought back for Tanks, to allow us to make these small upgrades, while keeping "exploity" total conversions prohibitively expensive.