I just looked at the website. The SP3 sale is through October 10, so the SP4 should be announced by then and the sale will still be on.
Also, the i3 SP3 is marked down to $649, which is the lowest price I've ever seen for that model. That should make the i3 model attractive for some people who are considering the S3. BTW, the i3 is not much faster than the S3 based on their GeekBench scores. The highest scores for the i3 are 1680 and 3569, verses 1025 and 3494 for the S3.
That may be a little deceptive. the key here is 1680 vs 1025. i.e. a single thread on an i3 is nearly 30% faster but in a bursty world the race to idle is king getting more small tasks done more quickly.
The Anandtech review contains a good number of benchmarks where the SP3 i3 and S3 x7 results are shown.
The Surface 3 Review
Kraken 1.1 lower is better: I3 2801, X7 4007
Octane v2 higher is better: i3 11,636, X7 8205
Webxprt higher is better: i3 972, X7 677
Pcmark 8H higher is better i3 1869, X7 1546
Pcmark 8C higher is better i3 1894, X7 1744 *note more graphically oriented is closer
Pcmark 8W higher is better i3 2346, X7 1250
... it continues with the i3 beating the X7 on every test, quite handily in most cases, it also draws pore power and runs hotter as the price for performance.