The introductory DVR fee for a Hopper Duo has always been $5 per month as far as I know. So, this is nothing new. After two years, that fee will go up to $10 per month. If you lease a Hopper With Sling, the introductory DVR fee would be $10 per month for two years. I am not sure that they would honor that introductory DVR rate if you add your own purchased Hopper With Sling after signing up.
As dishdude said, Dish will not allow both the Hopper With Sling and Hopper Duo to be active on the same account at the same time. (I know because I sold a Hopper Duo to someone who already had a Hopper With Sling, who ended up returning the Hopper Duo to me since they couldn't use it.) Dish does not allow the receivers with different DVR fees to be mixed on the same account, likely just to avoid any billing confusion about which DVR fee should be charged. The DVR fee is an account-level fee, not a separate fee for each DVR on the account. In any event, after using a Hopper With Sling, you probably wouldn't want a Hopper Duo anyway. Switching to a Hopper Duo would be a disappointing experience, considering how many features are missing on the Hopper Duo, that are available on the Hopper With Sling.
Keep in mind that there will likely be a one-time non-refundable $25 fee for leasing a Hopper Duo. This fee will not be disclosed to you until after the Hopper Duo is already installed, when it is too late to avoid that fee. (At least, that is what Dish did to me when I leased a Hopper Duo.) Then, when you activate your Hopper With Sling, you will have to deactivate the leased Hopper Duo and return it to Dish. So, it is probably better to simply not fool around with the Hopper Duo in the first place.
The last time I had more than one Hopper Duo active on my account at the same time (both Hopper Duos were purchased) the monthly fee for the additional Hopper Duo was $15. That second Hopper Duo fee has not changed since then (at least, according to the new fee chart). So, even if Dish did allow the Hopper With Sling and Hopper Duo to both be active at the same time, they would likely charge you the higher $10 (introductory) or $15 (full-price) Hopper With Sling DVR fee + the $15 fee for the Hopper Duo as a second receiver. So, that would be a total of $25 (or $30, depending on which DVR fee they charge) in fees for having both receivers active. If you are paying that much per month, you might as well just add a second Hopper With Sling instead of the Hopper Duo.
The DVR fee for the Hopper With Sling would be the same regardless of whether or not you are leasing the first one. However, by leasing one when you sign up, you can guarantee that you will get the $10 per month rate for the DVR fee for the first two years. Adding the purchased Hopper With Sling after that would be only the $5 per month that the new fee chart states for purchased equipment. So, two Hopper With Slings would be a total of $15 per month (with the introductory DVR fee) or $20 per month full-price.