Unless they remove other iPhone 8 features (like 3D Touch, P3 colour gamut, wireless charging), there will be no point in keeping the iPhone 8 in the line-up. Otherwise they would have to sell the SE2 at a higher price than the iPhone 8 (either pricing the SE2 higher than the current iPhone 8 price or cutting the price of the latter further).So it would be better than iPhone 8, but with a similar design. What's the point in having both? If they just want to sell a "cheap" iPhone they can cut the price of 8 and call it a day.
But the case against just keeping the iPhone 8 at its current price point or cutting its price further is that an iPhone SE2 with an A13 would be much more powerful and long-lasting from a performance and support status than the iPhone 8 with its A11 (two more years more long-lasting to be exact).