By that you mean the margin? Well the margin is largely depending on competition (or the lack thereof), isn't it? That's why I think a big player could make a difference iff they put their weight into it.
Not necessarily margin, rather non-recurring engineering costs (fab masks, design, software development), marketing, sales, administration, other overhead. You need massively higher demand in order to lower those costs, which won't happen only because Intel is entering the market. Instead, you'd need to significantly change the principles and trade-offs of FPGAs, for which I don't see any indications.
Here's how I see FPGA in a perfect world: You have an x86 compiler that finds, through static analysis, a subset of your program that fits nicely on your FPGA, and according to performance models leads to a good speedup. This program is then automatically passed on to the FPGA compiler. So for the novice programmer the thing is just a black box, enabled by some compiler flag. Furthermore you can steer the compiler through usage of compiler directives such as OpenMP or OpenACC. We know that FPGA compilation takes a long time, so the problem here is fixing mistakes - every iteration may potentially cost you hours, which AFAIK is what makes FPGA programming so costly. Therefore the static analysis has to be of very high quality and the auto-offloading should be conservative. This sort of thing IMO could significantly change the popularity of FPGA, thus offsetting the R&D costs.
Why would it? The price of an FPGA is not really determined by its production cost – for medium-size Xilinx FPGAs for example, the ratio of price/chip production cost is on the order of 50.