There are 2 primary aspects that needs to be considered in such cases.
First is the previous products and their sales as well as stockouts rate for Q4.
In projecting this, one might take a look at sales figures on similar period to see if there is any cyclical elements coming into play (e.g. sales always increase on Q4 as the products are particularly popular for Christmas or New Year's Eve). Another way is to see the month-to-month or quarter-to-quarter growth rate and extrapolated them to Q4.
Another thing that needs to be taken into account is whether the new product line potentially introduces any cannibalization towards the existing product lines. Take a look at the customer segment targets and their behavior along with the nature of the product tiself to ascertain this.
Second is the potential sales of the new product line.
Assuming the existing product lines parameters stays the same and no cannibalization occured, then revenue improvement will be solely determined by the new product line sales.
If there are changes on the existing products and cannibalization occurs, the new product sales must compensate for the difference.
Before trying to estimate the number, try to calculate the sales figure by assuming all products will be sold. See if the revenue improvement objective is within the range under the maximum number of sales of new product lines. If it is within the range, proceed to estimate the sales figure. If not, then the question lies on more on whether more products should be produced as well as other initiatives to fulfill the improvement goal.
In order to estimate the sales, take into account the target customer segment's preferences and how the new product line is fulfilling them (in terms of needs, pricings, distribution channels, etc). Look at the market and see if there is any equivalent product with apparent traction (either similar product sold by competitors or subsitutes in case of a novel product). Use these informations to estimate potential sales number.
Combining the figures from the 2 spects will give the final number, which will lead to the answer on whether the new product introduction increases revenue by the targeted rate.
Hope it helps.