RxJava - Opposite of switchMap() Operator?

Sure, gate the processing of a value by a boolean that is set after the processing finished:

AtomicBoolean gate = new AtomicBoolean(true);

Observable.interval(200, TimeUnit.MILLISECONDS)
.flatMap(v -> {
    if (gate.get()) {
        gate.set(false);

        return Observable.just(v).delay(500, TimeUnit.MILLISECONDS)
                .doAfterTerminate(() -> gate.set(true));
    } else {
        return Observable.empty();
    }
})
.take(10)
.toBlocking()
.subscribe(System.out::println, Throwable::printStackTrace);

Edit

Alternative:

Observable.interval(200, TimeUnit.MILLISECONDS)
.onBackpressureDrop()
.flatMap(v -> {
    return Observable.just(v).delay(500, TimeUnit.MILLISECONDS);
}, 1)
.take(10)
.toBlocking()
.subscribe(System.out::println, Throwable::printStackTrace);

You can change onBackpressureDrop to onBackpressureLatest to continue immediately with the latest value.

I know that this an old thread but currently there is a RxJs operator that does just that.

The operator is exhaustMap.

According to the docs:

ExhaustMap projects each source value to an Observable which is merged in the output Observable only if the previous projected Observable has completed.

Docs example:

import { fromEvent, interval } from 'rxjs';
import { exhaustMap, take } from 'rxjs/operators';

const clicks = fromEvent(document, 'click');
const result = clicks.pipe(
  exhaustMap(ev => interval(1000).pipe(take(5)))
);
result.subscribe(x => console.log(x));